Optical air data system

ABSTRACT

At least one second beam of light from a first beam of light generated by a laser is directed into an atmosphere. Light therefrom scattered by molecules or aerosols in the atmosphere is collected by at least one telescope as at least one light signal, which together with a reference beam from the first beam of light are simultaneously processed by an interferometer, and resulting fringe patterns are imaged onto a detector adapted to output a resulting at least one signal responsive thereto. In various aspects: a plurality of transversely separated light collectors collected the scattered light; at least two telescopes are associated with a common second beam of light; or the telescope is coupled to a gimble mount that provides for positioning a region of overlap of the second beam of light with the field of view of the telescope.

CROSS-REFERENCE TO RELATED APPLICATIONS

The instant application is a continuation of U.S. application Ser. No.11/460,603, filed on Jul. 27, 2006, which is a continuation-in-part ofU.S. application Ser. No. 10/366,910, filed on Feb. 14, 2003, now U.S.Pat. No. 7,106,447, which issued on Sep. 12, 2006, and which claims abenefit of priority from U.S. Provisional Application Ser. No.60/360,818, filed on Mar. 1, 2002. U.S. application Ser. No. 11/460,603also claims a benefit of priority from U.S. Provisional Application Ser.No. 60/596,531, filed on Oct. 3, 2005. The entire content of each of theabove-identified applications is incorporated herein by reference.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

This invention was made with Government support under Contract No.F33615-92-D-3602 awarded by the Flight Dynamics Directorate, WrightLaboratory, Air Force Materiel Command (ASC), United States Air Force,Wright-Patterson AFB OHIO 45433-6553. The Government has certain rightsin this invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a schematic block diagram of a molecular optical airdata system;

FIG. 2 a illustrates several opto-mechanical elements of an optical airdata system;

FIG. 2 b illustrates a geometry of an embodiment of an optical head ofan optical air data system;

FIG. 3 illustrates an optical head of a biaxial system;

FIG. 4 illustrates an optical head of a coaxial system;

FIG. 5 a illustrates an isometric view of a Fabry-Pérot interferometer;

FIG. 5 b illustrates a side view of the Fabry-Pérot interferometerillustrated in FIG. 5 a for one associated fiber-optic input and acorresponding output.

FIG. 6 illustrates a solid Fabry-Pérot etalon;

FIG. 7 a illustrates fringes from a fully-illuminated Fabry-Pérotetalon;

FIG. 7 b illustrates fringes from a Fabry-Pérot etalon illuminated withfour fiber input channels;

FIG. 8 illustrates four channels of fringes being collapsed by a quadcircle-to-line interferometer optic (quad-CLIO) to four lines in theshape of a cross-pattern on an opto-electric detector;

FIG. 9 illustrates a prior art circle-to-line interferometer optic(CLIO);

FIG. 10 illustrates the operation of a circle-to-line interferometeroptic (CLIO);

FIG. 11 illustrates a side view of a quad-CLIO element and an associateddetector;

FIG. 12 illustrates a plan view of the quad-CLIO element illustrated inFIG. 11, viewed from the side of an associated first pyramidal shapedoptic element;

FIG. 13 illustrates a plan view of the quad-CLIO element illustrated inFIG. 11, viewed from the side of an associated second pyramidal shapedoptic element;

FIG. 14 illustrates a fragmentary end view of a concave conicalreflector on a face of the first pyramidal shaped optic elementillustrated in FIGS. 11 and 12, wherein the direction of the end view issubstantially parallel to the face of the first pyramidal shaped opticelement;

FIGS. 15 a and 15 b illustrate a cross-binning process operating on across-pattern from a quad-CLIO element;

FIGS. 16 a and 16 b illustrate a circular process operating on a fringepattern from a Fabry-Pérot interferometer;

FIG. 17 illustrates an image of a set of circular fringe patterns andregions of interest associated with a circular binning process;

FIG. 18 a illustrates a flow chart of a first embodiment of a circularbinning process;

FIG. 18 b illustrates an alternate decision block of the firstembodiment of a circular binning process illustrated in FIG. 18 a;

FIG. 19 illustrates a flow chart of a second embodiment of a circularbinning process;

FIG. 20 illustrates a block diagram of various optical air data systemembodiments;

FIG. 21 illustrates an exploded view of a thermal chamber assemblyenclosing a Fabry-Pérot etalon;

FIG. 22 illustrates a first exploded view of a core assemblyincorporated in the thermal chamber assembly illustrated in FIG. 21;

FIG. 23 illustrates a second exploded view of the core assemblyincorporated in the thermal chamber assembly illustrated in FIG. 21;

FIG. 24 illustrates a third exploded view of the core assemblyincorporated in the thermal chamber assembly illustrated in FIG. 21;

FIG. 25 illustrates a physical layout of various optical air data systemembodiments;

FIG. 26 illustrates an end view of a fiber-optic assembly connected tothe input of the Fabry-Pérot interferometer illustrated in FIG. 25;

FIG. 27 illustrates a view of a set of circular fringe patterns imagedonto the detector of the optical air data system illustrated in FIG. 25for an embodiment that does not incorporate a quad-CLIO;

FIG. 28 illustrates a view of a set of substantially linear fringepatterns imaged onto the detector of the optical air data systemillustrated in FIG. 25 for an embodiment that incorporates a quad-CLIO;

FIG. 29 illustrates fringes from the Fabry-Pérot etalon from twoscattered signals associated with different velocities;

FIG. 30 illustrates a block diagram of an optical air data system dataanalysis process;

FIG. 31 illustrates a fringe associated with a signal channel processedby the Fabry-Pérot etalon, wherein the fringe comprises an aerosol(Mie), molecular (Rayleigh) and background signal components;

FIG. 32 illustrates a periodic transmission function of a Fabry-Pérotetalon;

FIG. 33 illustrates a flow chart of a process for determining opticalair data system measured air data products;

FIG. 34 illustrates a flow chart of a process for determining opticalair data system derived air data products;

FIG. 35 illustrates a side-view of a signal processor of an optical airdata system, including a bi-CLIO element, adapted to provide formeasuring wavelength as a function of range;

FIG. 36 illustrates a plan view of the bi-CLIO element illustrated inFIG. 35, viewed from the perspective of an associated first pyramidalshaped optic element;

FIG. 37 illustrates a fragmentary end view of a concave conicalreflector on a face of the first pyramidal shaped optic element of thebi-CLIO element illustrated in FIGS. 35 and 36, wherein the direction ofthe end view is substantially parallel to the face of the firstpyramidal shaped optic element;

FIG. 38 illustrates a plan view of the bi-CLIO element illustrated inFIG. 35, viewed from the perspective of an associated second pyramidalshaped optic element;

FIG. 39 illustrates a fragmentary end view of a reflective surface on aface of the first second shaped optic element of the bi-CLIO elementillustrated in FIGS. 35 and 38, wherein the direction of the end view issubstantially parallel to the face of the second pyramidal shaped opticelement;

FIG. 40 illustrates a plan view of a CCD detector illustrated in FIG.35, and an associated imaging process;

FIG. 41 illustrates an image from the CCD detector illustrated in FIG.40;

FIG. 42 illustrates a flow chart of a first imaging process forgenerating range-resolved images;

FIG. 43 a illustrates a plan view of a CCD detector in an initial state;

FIG. 43 b illustrates a plan view of the CCD detector at the beginningstage of an image recording cycle;

FIG. 43 c illustrates a plan view of the CCD detector at an intermediatestage of the image recording cycle;

FIG. 43 d illustrates a plan view of the CCD detector at a final stageof the image recording cycle;

FIG. 43 e illustrates an image transferred from the CCD detector;

FIG. 44 illustrates a flow chart of a second imaging process forgenerating range-resolved images;

FIG. 45 illustrates various embodiments for multiplexing reference andsignal channels for a range-resolved optical air data system;

FIG. 46 illustrates various interaction regions associated with a commonline of sight of a second laser beam;

FIG. 47 illustrates an alternative to the various embodimentsillustrated in FIG. 46, suitable for determining air data products thatare not dependent upon relative wind velocity;

FIG. 48 illustrates a laser coupled with a fiber optic to an associatedharmonic generator, the output of which is then propagated in freespace;

FIG. 49 a illustrates a first embodiment of a laser coupled with a fiberoptic to a plurality of harmonic generators in series for generating afourth harmonic;

FIG. 49 b illustrates a second embodiment of a laser coupled with afiber optic to a plurality of harmonic generators in series forgenerating a third harmonic;

FIG. 49 c illustrates a third embodiment of a laser coupled with a firstfiber optic to a first harmonic generator, the latter of which isconnected to a second harmonic generator with a second fiber optic;

FIG. 49 d illustrates a fourth embodiment of a laser coupled to a firstharmonic generator, the latter of which is connected to a secondharmonic generator with a fiber optic;

FIG. 50 illustrates various applications of an optical air data system;and

FIG. 51 illustrates a gimbal mechanism operatively associated with anoptical air data system.

DESCRIPTION OF EMBODIMENT(S)

Referring to FIG. 1, an optical air data system 10 comprises a laser 12that generates a first laser beam 14 which is split into a referencebeam 16 and one or more second laser beams 18 by a beam splitter optic20 in an optical head 22. The optical head 22 provides for directing theone or more second laser beams 18 into an atmosphere 24 within sightthereof, and further incorporates a corresponding one or more telescopes26, each associated with one of the one or more second laser beams 18,wherein each of the telescopes 26 provides for receiving light 28 thatis backscattered by the atmosphere 24 from a corresponding interactionregion 30 therein defined by the intersection of the associated secondlaser beam 18 with an associated field of view 32 of the correspondingtelescope 26.

For example, in one embodiment, the first 14 and second 18 laser beamscomprise ultraviolet (UV) laser light at a wavelength of about 266 nmthat is emitted in three directions from surface-mounted apertures 34,for example, flush with a surface 36 of an aircraft 38, and theassociated one or more telescopes 26 provide for detecting the returnfrom scattering of the one or more second laser beams 18 by atmosphericmolecules and aerosols. A wavelength of about 266 nm, being invisible tothe human eye and substantially absorbed by the atmosphere, isbeneficial for its stealth, eye safety and molecular scatteringproperties. There is very little natural background light due toabsorption of most natural 266 nm light by ozone and molecular oxygen.Ultraviolet light at about 266 nm is readily absorbed by glass andplastic, such as used in aircraft wind screens, which provides forimproved eye safety. The particular operating wavelength of the opticalair data system 10 is not limiting, and it should be understood that anyoptical wavelength that interacts with that which is being sensed in theassociated interaction region 30 may be used.

Referring to FIGS. 2 a and 2 b, the optical head 22 provides fordirecting the outgoing one or more second laser beams 18, as well ascollecting the backscattered signal, i.e. light 28, utilizing thecorresponding associated separate telescopes 26. The optical head 22 canbe custom-configured. For example, as illustrated in FIGS. 2 a and 2 b,proximate to the center of the optical head 22, the first laser beam 14is divided using a beam splitter optic 20 into three separate secondlaser beams 18.1, 18.2 and 18.3, and then directed along threeassociated lines of sight 40: 40.1, 40.2 and 40.3, each spaced 120degrees from each other and 30 degrees from a central axis 42. Lightsignals 44 are then collected by each telescope 26 of an array of threetelescopes 26 built into the optical head 22. Plural channels orientedin different directions provide for calculating a wind or airspeedvector from the associated light signals 44, in addition to scalarproperties of the atmosphere 24 in the associated interaction regions 30along the associated lines of sight 40.

Each second laser beam 18 and its associated telescope 26 define achannel, and neither the number of channels, nor the geometry of thechannels in relation to each other, is limiting. For example, althoughthe embodiment illustrated in FIGS. 2 a and 2 b incorporates threechannels, spaced 120 degrees apart from each other, other angles may beused to calculate a wind or airspeed vector. In addition, although threechannels are necessary to calculate a wind or airspeed vector in 3-Dspace, the system may have extra redundant channels, dual channels tomeasure wind or airspeed in a particular plane, or single channels tomeasure the speed or properties of the atmosphere 24 along a specificline of sight of the associated telescope 26.

The optical air data system 10 is a laser remote sensing instrument thatsenses within the volume of the interaction region 30. The range 46 tothe interaction region 30, e.g. the distance thereof from the surface 36of the aircraft 38, is defined by the geometry of the associated secondlaser beam 18 and the corresponding telescope 26 as embodied in theoptical head 22. The range 46 within the interaction region 30 canoptionally be further resolved with associated temporal range gating, orrange-resolved imaging, of the associated light signals 44 if desired ornecessary for a particular application.

The optical air data system 10 is responsive substantially only toscattering from the interaction region 30 where the field of view 32 ofthe detecting telescope 26 and the second laser beam 18 overlap, and thegeometry of the optical head 22 can be adapted to locate the interactionregion 30 at substantially any distance, e.g. near or far, from theoptical head 22 provided there is sufficient backscattered light 28 tobe subsequently processed. For example, with the optical head 22 adaptedto locate the interaction region 30 relatively far from the surface 36of an aircraft 38, e.g. so as to be substantially not influenced by theturbulent region surrounding the aircraft 38, there would besubstantially no signal from the associated near-field region 48relatively proximate to the surface 36 of the aircraft 38 that wouldotherwise be affected, e.g. adversely, by the turbulent air streamtherein.

Referring to FIGS. 1, 2 a, 2 b and 3, in accordance with a first aspect,each channel of the optical head 22.1 is adapted as a biaxial system 50wherein, for a given channel, the associated second laser beam 18 andtelescope 26 do not share a common axis. For example, at the opticalhead 22.1, the respective axes 52, 54 of the second laser beam 18 andtelescope 26 are separated by an offset distance 56, and the axes 52, 54are oriented at a relative angle 58 and directed so that the secondlaser beam 18 intersects the field of view 32 of the telescope 26 so asto define the associated interaction region 30. The length 60 of theinteraction region 30 is defined between an entrance 62 where the secondlaser beam 18 enters the field of view 32 of the telescope 26, and anexit 64 where the second laser beam 18 exits the field of view 32 of thetelescope 26, wherein the interaction region 30 is bounded by the secondlaser beam 18 between the associated entrance 62 and exit 64.

Referring to FIG. 4, in accordance with a second aspect, the opticalhead 22.2 is adapted as a coaxial system 66 wherein, for a givenchannel, the associated second laser beam 18 and telescope 26substantially share a common axis 52, 54. For example, a mirror 68located within a portion, e.g. a central portion, of the field of view32 of the telescope 26. The second laser beam 18 is reflected off themirror 68, and the mirror 68 is oriented so as to substantially alignthe axis 52 of the second laser beam 18 reflected from the mirror 68,with the axis 54 of the telescope 26. The mirror 68 partially obstructsthe field of view 32 of the telescope 26, which provides for anear-field region 48 in the shadow 70 of the mirror 68 within which thesecond laser beam 18 is not visible to the telescope 26 and thereforeoutside the interaction region 30, thereby providing for substantiallypreventing any signal return from a prospective turbulent regionproximate to the surface 36 of the aircraft 38 for an optical air datasystem 10 operatively associated therewith. The interaction region 30extends from an entrance 62 where the size of second laser beam 18exceeds the size of the shadow 70 in the near-field region 48, andtherebeyond the interaction region 30 remains within the field of view32 of the telescope 26. The interaction region 30 can then be tuned byadjusting the size of the central obstruction, the field of view 32 ofthe telescope 26, the divergence angle of the second laser beam 18, andby translating a final light-collecting element 72 of the telescope 26along the axis 54 thereof so as to effectively change the field of view32 of the telescope 26 and the focal plane for the finallight-collecting element 72.

Each telescope 26 comprises a lens system 74, and the light signal 44collected thereby is collected by the final light-collecting element 72thereof into a fiber optic 76 that directs the returned photons toassociated portions of a Fabry-Pérot interferometer 78 and an associateddetection system 80 for processing thereby. The reference beam 16 fromthe laser 12 and beam splitter optic 20 is directed to a separateportion of the Fabry-Pérot interferometer 78 and an associated detectionsystem 80 for simultaneous processing thereby.

The reference beam 16 and the light signal 44 from the lens system 74are each collimated by a collimating lens 82 of the Fabry-Pérotinterferometer 78 and then filtered by a filter system 84 which, forexample, as illustrated in FIG. 2 a, incorporates eight bandpass filtermirrors 86 having associated filter pass bands centered about theoperating frequency of the laser 12—e.g. about 266 nm for theabove-described embodiment—which provides for filtering out associatedbackground light. The filter system 84 exhibits high out-of-bandrejection, as well as low in-band attenuation, and the bandwidth of thefilter system 84 is sufficiently narrow so as to substantially filter orremove components of solar radiation or stray light in the collectedlight signals 44, yet sufficiently broad so as to be substantiallylarger than the bandwidth of the thermally-broadened spectrum incombination with the largest expected associated Doppler shift. Forexample, in one embodiment, the filter system 84 is adapted so as toprovide for maximum filtering of light frequencies that are outside thefrequency band of interest, e.g. greater than about 2 nanometers aboveor below the nominal center frequency of the first laser beam 14.

Referring to FIGS. 1, 2 a, 5 a, 5 b, 7 a and 7 b the light signals 88from the filter system 84 are input to a Fabry-Pérot etalon 90 of theFabry-Pérot interferometer 78, which provides for generating a fringepattern 92 responsive to the optical frequency of the associated lightsignals 88, which optical frequency can exhibit a Doppler shiftresponsive to a relative velocity of the atmosphere 24 within theinteraction region 30 from which the associated light 28 isbackscattered. The Fabry-Pérot etalon 90 of the Fabry-Pérotinterferometer 78 comprises first 94 and second 96 partially-reflectivesurfaces which are parallel to one another and separated by a fixed gap98, and located between the collimating lens 82 and associated imagingoptics 100. Light 102 at a focal plane 104 of the collimating lens 82 issubstantially collimated thereby, and the angles at which the light 102is passed through the Fabry-Pérot etalon 90 is dependent upon theoptical frequency of the light 102, which, referring to FIG. 7 a,becomes imaged as a circular fringe pattern 106—also known as Haidingerfringes—comprising a plurality of concentric circular fringes 108 in thefocal plane 110 of the imaging optics 100. Referring to FIG. 7 a, for afully-illuminated Fabry-Pérot etalon 90, the resulting circular fringepattern 106 is in the form of closed concentric circles centered aboutthe optic axis 112 of the imaging optics 100.

For example, in the embodiment illustrated in FIGS. 1, 5 a and 5 b, theFabry-Pérot etalon 90 comprises a pair of planar optical windows 114—forexample, constructed of either optical glass or fused quartz—alignedparallel to and facing one another and spaced apart from one another bya gap 98, wherein, for example, the first 94 and second 96partially-reflective surfaces are on separate facing surfaces of theplanar optical windows 114, e.g. partially-silvered surfaces or otherpartially-reflective surfaces. Alternatively, the first 94 and second 96partially-reflective surfaces could be on the outside opposing faces ofthe planar optical windows 114, or one of the first 94 and second 96partially-reflective surfaces could be on a inner facing surface of oneof the planar optical windows 114, and the other of the first 94 andsecond 96 partially-reflective surfaces could be on a outer facingsurface of the other of the planar optical windows 114. In oneembodiment, the gap 98 is substantially fixed, whereas in otherembodiments, the gap 98 is moveable, e.g. adjustable, so as to providefor a tunable Fabry-Pérot etalon 90.

Referring to FIG. 6, alternatively, the Fabry-Pérot etalon 90 couldcomprise a solid optical element 116—for example, constructed of eitheroptical glass or fused quartz—with planar parallel faces 118 comprisingfirst 94 and second 96 partially-reflective surfaces separated by a gap98.1 constituting the length of the solid optical element 116.

Referring to FIGS. 5 a and 5 b, the optical air data system 10 providesfor an efficient use of the Fabry-Pérot etalon 90 by simultaneouslyprocessing a plurality of different channels of light 102 with a single,common Fabry-Pérot etalon 90. In one embodiment, a single Fabry-Pérotetalon 90 is used with four channels of light 102, i.e. a referencechannel 120 from the reference beam 16, and three signal channels 122.1,122.2 and 122.3 from the associated three lens systems 74.1, 74.2 and74.3 associated with each of three telescopes 26.1, 26.2 and 26.3 havingrespectively three different lines of sight 40.1, 40.2 and 40.3.Referring also to FIG. 2 a, respective fiber optics 76.1, 76.2, 76.3 and76.4 receive light from the reference beam 16 and from each of the lenssystems 74.1, 74.2 and 74.3, respectively, and illuminate correspondingportions of the Fabry-Pérot etalon 90 from respective off-axis locations124.1, 124.2, 124.3 and 124.4 in the focal plane 104 of the collimatinglens 82, producing associated images of partial circular fringe patterns106.1, 106.2, 106.3 and 106.4, for example, as illustrated in FIGS. 5 aand 7 b.

The off-axis illumination of the Fabry-Pérot etalon 90 provides forincreasing the geometric etendue of the optical air data system 10 thanwould result otherwise, wherein geometric etendue G characterizes theability of an optical system to accept light. Geometric etendue G isdefined as a product of the area A of the emitting source and the solidangle Ω into which the light therefrom propagates, i.e. (G=A*Ω).Geometric etendue G is a constant of the optical system, and isdetermined by the least optimized portion thereof. For a fixeddivergence and aperture size of the associated fiber optic 76, for agiven value of geometric etendue G, the area A of the emitting source(i.e. that of the fiber optic 76)—and the associated diameter of theoptical system—may be reduced by increasing the solid angle Ω, i.e. thedivergence of the associated optical system, so as to provide forreducing the size of the associated optical system without sacrificingperformance. Alternatively, for a given area A and associated diameterof the optical system, the geometric etendue G of the optical system maybe increased by increasing the solid angle Ω. For a Fabry-Pérotinterferometer 78, increasing the angular divergence, i.e. solid angleΩ, of the associated optical system provides for a greater fractionand/or number of circular fringes 108. The optical air data system 10simultaneously processes a reference channel 120 and one or more signalchannels 122.1, 122.2 and 122.3 using a common Fabry-Pérot etalon 90,each channel 120, 122.1, 122.2 and 122.3 occupying a separate portion ofthe Fabry-Pérot etalon 90, the collection of channels 120, 122.1, 122.2and 122.3 thereby necessitating a larger-diameter Fabry-Pérot etalon 90than would be required otherwise if only a single channel 120, 122.1,122.2 or 122.3 were to be processed thereby. Accordingly associatedrespective off-axis locations 124.1, 124.2, 124.3 and 124.4 of therespective fiber optics 76.1, 76.2, 76.3 and 76.4 provides for bothsimultaneously accommodating the plurality of fiber optics 76.1, 76.2,76.3 and 76.4 input to the common Fabry-Pérot etalon 90, and providesfor increasing the associated angular divergence through the opticalsystem which provides for either relatively increasing the geometricetendue G and associated light gathering capability of the of theassociated optical system for a given-sized optical system, or forrelatively decreasing the size (i.e. diameter) of the optical system fora given geometric etendue G thereof.

Signals from the signal channel 122.1, 122.2 or 122.3 for each of theassociated interaction regions 30 are substantially simultaneouslyprocessed together with a signal from the reference channel 120 so as toprovide for calibrating, and maintaining the calibration of, the opticalair data system 10, and so as to provide for determining the associatedair data products such as the speed, temperature and density of theatmosphere 24. This provides for an inherent self-calibration of theassociated measurements or quantities derived therefrom. If wavelengthdrift of the first laser beam 14 is not otherwise accounted for in thedata, then errors can arise when making a measurement of the Dopplershift and resulting wavelength shift of the signal channels 122.1, 122.2and 122.3. The optical air data system 10 provides for automaticallycompensating for wavelength drift of the first laser beam 14 from thedata because each measurement from a signal channel 122.1, 122.2 or122.3 is corrected using a corresponding measurement from the referencechannel 120 associated with the reference beam 16.

Referring to FIG. 8, in one embodiment, a quad circle-to-lineinterferometer optic 126 (quad-CLIO 126) is used to transform the fourchannels 120, 122.1, 122.2 and 122.3 of circular fringe patterns 106.1,106.2, 106.3 and 106.4 into four associated linear fringe patterns128.1, 128.2, 128.3 and 128.4, forming a cross pattern 130. Thequad-CLIO 126 comprises four circle-to-line interferometer optic 132(CLIO 132) elements, each associated with a different one of the fourchannels 120, 122.1, 122.2 and 122.3 of circular fringe patterns 106.1,106.2, 106.3 and 106.4.

Referring to FIG. 9, a circle-to-line interferometer optic 132 (CLIO132), described in U.S. Pat. No. 4,893,003, the entire content of whichis incorporated herein by reference, comprises a concave conicalreflector 134, the surface of which is a conical segment constituting asection of the underlying conical surface. Electromagnetic energy 136from the Fabry-Pérot interferometer 78—constituting the circular fringepattern 106 to be transformed—is propagated substantially parallel tothe conical axis 138 of the underlying conical surface, and is reflectedand focused by the concave conical reflector 134 substantially onto alinear detector 140 substantially along or proximate to the conical axis138. In one embodiment, the apex 142 of the underlying conical surfaceis situated where the conical axis 138 intersects the focal plane 110 ofthe circular fringe pattern 106. Referring to FIG. 10, the CLIO 132transforms each circular fringe 108, e.g. 108.1, 108.2, 108.3, 108.4 and108.5, into a corresponding spot 144, e.g. 144.1, 144.2, 144.3, 144.4and 144.5 of an associated linear fringe pattern 128, therebyconcentrating the associated electromagnetic energy 136 so as to improvethe associated signal to noise ratio of the associated detection processby the associated linear detector 140. Accordingly, each CLIO 132provides for transforming a circular fringe pattern 106 into acorresponding linear fringe pattern 128 substantially along theassociated conical axis 138 so as to provide for using a linear detector140 array—for example, a charge-coupled device (CCD), e.g. as used inspectroscopic analysis—to detect the light of the linear fringe pattern128.

Referring to FIGS. 11-14, for example, in one embodiment, the quad-CLIO126, comprises a first pyramidal shaped optic element 146 whichcooperates with a plurality of corner reflector optic elements 148,which in turn cooperate with a second pyramidal shaped optic element150, all of which are operatively coupled to an associated base plate152. Each side face 154 of the first pyramidal shaped optic element 146incorporates an associated concave conical reflector 134 adapted toreceive an associated circular fringe pattern 106.1, 106.2, 106.3 and106.4 from the Fabry-Pérot interferometer 78, wherein different concaveconical reflectors 134 are adapted to receive different respectivecircular fringe patterns 106.1, 106.2, 106.3 and 106.4. A light signal88 of the circular fringe pattern 106.1, 106.2, 106.3, 106.4 isreflected from the corresponding concave conical reflector 134 onto afirst reflective surface 156 of a corresponding corner reflector opticelement 148, and then reflected therefrom onto a second reflectivesurface 158 of the corresponding corner reflector optic element 148, andthen reflected therefrom onto a third reflective surface 160 on a sideface 162 of the second pyramidal shaped optic element 150, and finallyreflected therefrom onto an associated detector 164, for example, anassociated array of linear detectors 140. For example, in oneembodiment, the first 156, second 158 and third 160 reflective surfacescomprise corresponding planar reflective surfaces 156′, 158′ and 160′.The first 146 and second 150 pyramidal shaped optic elements are securedto and aligned with one another on opposite faces 152.1, 152.2 of thebase plate 152, for example, with fasteners 166, e.g. machine screws,extending through associated counterbores 168 in the first pyramidalshaped optic element 146, through the base plate 152, and into thesecond pyramidal shaped optic element 150. The corner reflector opticelements 148 are fastened to tongue portions 170 of the base plate 152with associated fasteners 172, which provide for a rotational adjustmentof the corner reflector optic elements 148. The base plate 152 isadapted with a plurality of openings 174 so as to provide for opticalcommunication between the first 156 and second 158 reflective surfaces.Each corner reflector optic element 148 incorporates a pair of sideplates 176 which provide for shielding stray light and for improvedstructural integrity. In another embodiment, one or more cornerreflector optic elements 148 could be replaced with separate elementsfor each of the associated first 156 and second 158 reflective surfaces.The first 146 and second 150 pyramidal shaped optic elements and thecorner reflector optic elements 148 can be constructed from a variety ofmaterials—including, but not limited to, aluminum, stainless steel,copper-nickel alloy, glass or fused quartz—that can be adapted toincorporate associated reflective surfaces or coatings.

Accordingly, the quad-CLIO 126 comprises a tele-kaleidoscope having apredetermined arrangement of mirrors adapted to provide for compressingthe azimuthal angular extent of the partial circular fringe patterns106.1, 106.2, 106.3 and 106.4 into associated linear fringe patterns128.1, 128.2, 128.3 and 128.4 forming a cross pattern 130. The circularfringe patterns 106.1, 106.2, 106.3 and 106.4 generated by theFabry-Pérot interferometer 78 are transformed by the quad-CLIO 126 intoa linear cross pattern 130 which is then imaged onto a detector 164. Forexample, the detector 164 may comprise one or more charge-coupleddevices (CCD), i.e. a CCD detector 164.1, a set of linear arrays, one ormore photomultiplier tubes, a plurality of avalanche photo diodes, orany other multi-element detection device that converts photons toelectrons. For example, a CCD detector 164.1 can be adapted to below-light sensitive, and can provide for provide a low noise imagereadout. A quad-CLIO 126, although not essential, can provide forenhancing the associated signal to noise ratio, and by providing fordetection using readily-available linear-based detectors such as alinear array or CCD, can provide for improving the overall efficiencyand simplicity of the signal detection process.

Referring to FIGS. 15 a and 15 b, the detector 164 generates an imagesignal 178 of the cross pattern 130 transformed by the quad-CLIO 126,wherein the image signal 178 comprises an array of pixels 180. Theefficiency of the detection process can be increased by binning theimage signal 178 during the associated detection process, wherein theplurality pixel values of a plurality of adjacent pixels 180 arereplaced with a single sum of the plurality of pixel values. Forexample, for a Cartesian array of pixels 180, generally the binningprocess can operate in either of the associated Cartesian directions, orin both directions. For example, binning is a standard process for usewith CCD devices wherein pixel charges are summed together on chip, soas to provide for reducing the relative amount of read-noise associatedwith the analog-to-digital conversion (A/D) process that occurs whenpixel charges are read off of the CCD detector 164.1, for example, bysumming a plurality of rows of pixels 180 together so as to limit thenumber of rows or columns undergoing an A/D conversion.

Referring to FIGS. 15 a and 15 b, in accordance with a first embodiment,an optical air data system 10 incorporates a quad-CLIO 126 and acustom-binning pattern is utilized to efficiently detect the associatedcross pattern 130, using a cross-binning process that provides formulti-axis binning within selected sub-regions of interest on the CCDdetector 164.1. For the cross-binning algorithm, respective regions ofinterest 182.1, 182.2, 182.3 and 182.4 are defined for each respectivechannel 120, 122.1, 122.2 and 122.3 comprising one leg 184.1, 184.2,184.3, 184.4 of the associated cross pattern 130. Photo-electricgenerated charges collected on the CCD detector 164.1 within each regionof interest 182.1, 182.2, 182.3, 182.4 are binned, i.e. summed, by theCCD detector 164.1 for each channel 120, 122.1, 122.2 and 122.3 alongthe width 186 of the corresponding leg 184.1, 184.2, 184.3, 184.4 of theassociated cross pattern 130, so as to compress the array of pixels 180associated with each leg 184.1, 184.2, 184.3, 184.4 of the associatedcross pattern 130 into a corresponding line of binned pixels 188.1,188.2, 188.3, 188.4 of the same length as the corresponding leg 184.1,184.2, 184.3, 184.4, but only one binned pixel 190 wide, with the valueof each binned pixel 190 equal to the sum of the values of thecorresponding pixels 180 across the corresponding leg 184.1, 184.2,184.3, 184.4 at a position 192 along the leg 184.1, 184.2, 184.3, 184.4corresponding to the position 192 of the corresponding binned pixel 190along the corresponding line of binned pixels 188.1, 188.2, 188.3,188.4, thereby providing for reducing the overall read noise associatedwith reading the lines of binned pixels 188.1, 188.2, 188.3, 188.4relative to that associated with reading a greater number of pixels 180in the original legs 184.1, 184.2, 184.3, 184.4 of the associated crosspattern 130, because of the reduction in the number of pixels being readand the greater value of each binned pixel 190 relative to that of thecorresponding pixels 180 of the original image signal 178.

Referring to FIGS. 16 a and 16 b, in accordance with a secondembodiment, the optical air data system 10 is adapted so as to providefor directly processing the associated circular fringe patterns 106.1,106.2, 106.3 and 106.4 from the Fabry-Pérot interferometer 78 withoututilizing an associated quad-CLIO 126, whereby the circular fringepatterns 106.1, 106.2, 106.3 and 106.4 are imaged directly upon theassociated CCD detector 164.1, and a circular binning algorithm thensums all pixels 180 at a particular radius 194 from the common center196 of the circular fringe patterns 106.1, 106.2, 106.3 and 106.4. Forexample, the circular binning algorithm could be implemented by a dataprocessor 198—for example, in software therein—operatively coupled tothe associated CCD detector 164.1, or to an associated plurality of CCDdetectors 164.1, each adapted to detect one or more of the associatedcircular fringe patterns 106.1, 106.2, 106.3 and 106.4. Afteridentifying the center 196 of the circular fringe patterns 106.1, 106.2,106.3 and 106.4, the circular binning algorithm sums up the CCD charges(i.e. pixel values) for each pixel 180 at a particular radius from thecenter 196, for a particular circular fringe pattern 106.1, 106.2,106.3, 106.4, for each of the circular fringe patterns 106.1, 106.2,106.3 and 106.4, so as to provide a respective associated line of binnedpixels 188.1, 188.2, 188.3, 188.4 for each of the respective circularfringe patterns 106.1, 106.2, 106.3 and 106.4. Compared with the firstembodiment operative with a quad-CLIO 126 and an associatedcross-binning process operative within the CCD detectors 164.1, whereinthe charges for pixels 180 to be binned are summed before readout of theresulting corresponding binned pixel 190, the circular binning processof the second embodiment provides for reading the pixels 180 beforebinning, whereby each pixel 180 is read from the CCD detector 164.1 andconverted by an A/D conversion process, which results in a greateramount of overall read noise than would occur with the first embodiment,although the overall noise level can be kept to within acceptable levelsby using a relatively low-noise CCD detector 164.1. The ratio of signalto read noise can be enhanced by increasing the exposure time of the CCDdetector 164.1 between read cycles, although at the cost of reduceddynamic frequency response of the associated resulting air dataproducts.

Referring to FIG. 17, an image 200 of a set of circular fringe patterns106.1, 106.2, 106.3 and 106.4 comprises an array of N rows by M columnsof pixels 180, each of which is captured by an associated detector 164and stored in a memory 202 of the associated data processor 198 of theoptical air data system 10. The image 200 comprises four regions ofinterest (ROI) 204.1, 204.2, 204.3 and 204.4, each comprising a segment206 containing an associated circular fringe pattern 106.1, 106.2, 106.3and 106.4, and centered about the common center 196 of the circularfringe patterns 106.1, 106.2, 106.3 and 106.4, wherein the center 196 ofthe circular fringe patterns 106.1, 106.2, 106.3 and 106.4 is determinedupon initial calibration or subsequent recalibration of the associatedoptical air data system 10, and is assumed to be stationary during theoperation thereof. For example, the center 196 may be determined byrecording a substantial number, e.g. thousands, of circular fringepatterns 106.1, 106.2, 106.3 and 106.4 and determining the location ofthe center 196—by either iteration starting with an initial guess, orleast squares or correlation with the coordinates of the center 196 asunknowns to be determined—that provides for a best fit of the recordedcircular fringe patterns 106.1, 106.2, 106.3 and 106.4 with acorresponding circular model thereof centered at the center 196 of thecircular fringe patterns 106.1, 106.2, 106.3 and 106.4.

Referring to FIG. 18 a, in accordance with a first embodiment of acircular binning process 1800, in step (1802) a K×NROI bin arrayBIN(*,*) is defined with storage for NROI vectors of K elements each tohold the circumferentially-binned values for each of the NROI=4 circularfringe patterns 106.1, 106.2, 106.3 and 106.4, and each value thereof isinitialized to zero. Then, in steps (1804) and (1806), for each row i ofthe N rows, and for each column j of the M columns, of the pixels 180 inthe image 200, the value Pixel(i,j) of the pixel 180 is read from theimage 200 in step (1808), and in step (1810), the corresponding X and Ylocations thereof are calculated respectively as follows:x _(j) =j·α _(X) −x ₀y _(i) =i·α _(y) −y ₀  (1)wherein α_(X) and α_(Y) are the distances per pixel in the X and Ydirections, respectively, and x₀ and y₀ are the coordinates of thecenter 196 relative to Pixel(1,1) at the lower left corner of the image200. Then, in step (1812), the Cartesian coordinates (x_(j), y_(i)) fromstep (1810) are transformed to cylindrical coordinates (R, θ), asfollows:

$\begin{matrix}{{R = \sqrt{x_{j}^{2} + y_{i}^{2}}}{\theta = {{Tan}^{- 1}\left( \frac{y_{i}}{x_{j}} \right)}}} & (2)\end{matrix}$

Then, in step (1814), if the angle θ is within a region of interest(ROI) 204.1, 204.2, 204.3 and 204.4, the associated region of interestROI is identified, and in step (1816), the radial bin index k is givenby:

$\begin{matrix}{k = {\frac{R}{\beta} - k_{0}}} & (3)\end{matrix}$where β is the distance per pixel in the radial direction, and k₀ is thenumber of pixels 180 between the center 196 and the closest portion ofthe circular fringe pattern 106.1, 106.2, 106.3 and 106.4 closestthereto. Then, in step (1818), the associated value Pixel(i,j) of theassociated pixel 180 is added to the bin element BIN(k,ROI) of the binarray BIN(,) as follows:BIN(k,ROI)=BIN(k,ROI)+Pixel(i,j)  (4)

Then, or otherwise from step (1814), in step (1820), if all of thepixels 180 have been circumferentially binned, then, in step (1822), thecircumferentially-binned values for each of the circular fringe patterns106.1, 106.2, 106.3 and 106.4 are returned in the associated bin arrayBIN(*,NROI). Otherwise, the process repeats with steps (1804) and (1806)for each of the rows and columns of pixels 180 until all of the circularfringe patterns 106.1, 106.2, 106.3 and 106.4 are binned.

Referring to FIGS. 17 and 18 b, alternatively, regions of interest (ROI)204.1′, 204.2′, 204.3′ and 204.4′ may be defined by the correspondingrespective circular boundaries of the respective circular fringepatterns 106.1, 106.2, 106.3 and 106.4, in which case, step (1814) ofthe circular binning process 1800 would be replaced by step (1814′),whereby the test as to whether a particular pixel 180 was in aparticular regions of interest (ROI) 204.1 , 204.2′, 204.3′ and 204.4′would depend upon both cylindrical coordinates (R, θ) of the particularpixel 180.

Referring to FIG. 19, in accordance with a second embodiment of acircular binning process 1900, rather than processing every pixel 180 ofthe image 200, only those pixels 180 in predefined regions of interest(ROI) 204.1′, 204.2′, 204.3′ and 204.4′ are processed, wherein, forexample, the regions of interest (ROI) 204.1′, 204.2′, 204.3′ and 204.4′are defined by the corresponding respective circular boundaries of therespective circular fringe patterns 106.1, 106.2, 106.3 and 106.4.Beginning with step (1902), for each regions of interest (ROI) 204.1′,204.2′, 204.3′, 204.4′, in step (1904) the associated bin elementsBIN(*,ROI) are initialized to zero. Then, in step (1906), the number ofpixels 180 in the particular region of interest (ROI) 204.1′, 204.2′,204.3′, 204.4′ is given by the predetermined value of N(ROI). Then instep (1908), for pixel m of the N(ROI) pixels 180 in the particularregion of interest (ROI) 204.1′, 204.2′, 204.3′, 204.4′, thecorresponding column j and row i indexes for the particular pixel 180,corresponding to the associated X and Y locations thereof, are given instep (1910) by predetermined values from predetermined index arraysj(m,ROI) and i(m,ROI) respectively, and the corresponding element k ofthe associated bin array BIN(*,ROI) into which the particular pixel 180is to be binned is given by the predetermined index array k(m,ROI).Accordingly, in step (1912), the m^(th) pixel 180 is binned into thek^(th) element of the bin array BIN(*,ROI) as follows:BIN(k(m,ROI),ROI)=BIN(k(m,ROI),ROI)+Pixel(i(m,ROI),j(m,ROI))  (5)

Then, in step (1914), if all of the pixels m in the particular region ofinterest ROI have not been binned, then the process continues with step(1908). Otherwise, in step (1916), if all of the regions of interest(ROI) 204.1′, 204.2′, 204.3′ and 204.4′ have not been binned, then theprocess continues with step (1902). Otherwise, in step (1918), thecircumferentially-binned values for each of the circular fringe patterns106.1, 106.2, 106.3 and 106.4 are returned in the associated bin arrayBIN(*,NROI).

Referring to FIG. 20, in accordance with other embodiments, the opticalair data system 10 comprises a laser 12 that generates a first laserbeam 14 which is divided into a reference beam 16 and a second laserbeam 18 by a beam splitter optic 20. For example, in one embodiment, thelaser 12 comprises a Nd:YAG laser 12.1, which operates in a pulsed mode,and which is operatively associated with a laser seeder 208, forexample, a laser diode that provides for seeding the cavity of thepulsed Nd:YAG laser 12.1 with photons via an associated light couplingsystem, wherein the photons are injected from the laser seeder 208 intothe cavity of the Nd:YAG laser 12.1 prior to the build-up of the laserpulse associated of the first laser beam 14, causing the frequencythereof to substantially match that of the laser seeder 208, so as toprovide for substantially single-frequency operation. For example, inone embodiment, the laser seeder 208 is adapted in cooperation with theNd:YAG laser 12.1 so that the bandwidth of the first laser beam 14 is asnarrow or narrower than the bandwidth of the associated Fabry-Pérotinterferometer 78. The bandwidth of the Fabry-Pérot interferometer 78 isrelated to the finesse thereof. Beam steering optics 210, for example,incorporating beam splitting mirrors, prisms, a combination thereof, orsome other type of beam splitter, divide the second laser beam 18 into aplurality of second laser beams 18.1, 18.2 and 18.3, each directed in adifferent direction into the atmosphere 24. Corresponding associatedrespective telescopes 26.1, 26.2 and 26.3 each aimed so as to define anassociated respective interaction region 30.1, 30.2, 30.3 of therespective second laser beams 18.1, 18.2 and 18.3 projected into theatmosphere 24, collect the associated backscattered light signals 44from each of the respective interaction regions 30.1, 30.2, 30.3. Thelight signals 44 collected from each of the telescopes 26.1, 26.2 and26.3, and the reference beam 16 each illuminate, and are simultaneouslyprocessed by, a separate portion of a Fabry-Pérot interferometer 78,wherein the light signals 44 and reference beam 16 passing through theFabry-Pérot interferometer 78 are arranged with respect to one anotherin “cloverleaf” pattern. The light signals 44 and reference beam 16 areeach first collimated by a collimator 212, e.g. a collimating lens 82,then filtered by a filter system 84 as described hereinabove, and thenprocessed by an associated Fabry-Pérot etalon 90, the output of which isimaged by associated imaging optics 100 as associated circular fringepatterns 106.1, 106.2, 106.3 and 106.4 either directly onto a detector164, or into a quad-CLIO 126 which transforms the circular fringepattern 106.1, 106.2, 106.3 and 106.4 into a cross pattern 130 which isthen imaged onto the detector 164. The associated optical components areadapted for the frequency and power levels of operation. For example,for an optical air data system 10 incorporating a Nd:YAG laser 12.1operating at 355 nanometers, the optical elements would incorporateUV-grade fused silica substrates and standard anti-reflection coatingstuned for 355 nanometers.

The geometry of the circular fringe patterns 106.1, 106.2, 106.3 and106.4 from the Fabry-Pérot etalon 90 is responsive to the operative gap98, 98.1 thereof, which would vary with temperature if the associatedmaterial or materials controlling the length of the gap 98, 98.1 were toexhibit a non-zero coefficient of thermal expansion. Although thereference beam 16 simultaneously processed by the Fabry-Pérot etalon 90provides for compensating for thermal drift affecting all portions ofthe Fabry-Pérot etalon 90 equally, it is beneficial if the temperatureof the Fabry-Pérot etalon 90 can be controlled or maintained at aconstant level so as to prevent a thermal expansion or contractionthereof during the operation thereof. Accordingly, in accordance withone aspect of the optical air data system 10, the Fabry-Pérot etalon 90is thermally stabilized by enclosure in a thermally-controlled enclosure214 so as to prevent thermally-induced drift of the circular fringepattern 106.

In accordance with one aspect, the thermally-controlled enclosure 214 ispassive, for example, with the Fabry-Pérot etalon 90 enclosed, i.e.thermally insulated or isolated, using a material or materials with avery low thermal conductance to increase the thermal time constant andto prevent any substantial thermal shock from reaching the Fabry-Pérotetalon 90. In accordance with another embodiment, or in combinationtherewith, the thermally-controlled enclosure 214 is constructed from acombination of materials adapted so that there is negligible netcoefficient of thermal expansion in the portions of the structuresurrounding the Fabry-Pérot etalon 90 that affect the length of the gap98, 98.1.

Referring to FIGS. 21-24, in accordance with another aspect, atemperature of the thermally-controlled enclosure 214 is activelycontrolled responsive to at least one associated temperature sensor 216using a temperature controller 218 incorporating a feedback controlsystem 220 to control a heater, chiller or a combination heater andchiller—depending upon the temperature of the thermally-controlledenclosure 214 in relation to that of its environment. For example,referring to FIGS. 22 and 23, the Fabry-Pérot etalon 90 comprises asolid optical element 116—for example, constructed from high purityUV-grade fused silica—enclosed within a etalon mount 222 comprising acylindrical sleeve constructed from a material with a coefficient ofthermal expansion that closely matches that of the solid optical element116 so as to provide for preventing or substantially eliminatingunwanted thermally-induced radial stress in the solid optical element116. The etalon mount 222 in turn is surrounded by a plurality, e.g.three, heat sink segments 224, each having a relatively high thermalconductance—for example, constructed of copper—each comprising an innercylindrical face 226 that abuts an outside surface 228 of the etalonmount 222, and an outer face 230 incorporating a recess 232 adapted toreceive and abut a first surface 234 of a thermo-electric heat pump 236,for example, what is known as a thermoelectric cooler (TEC). Uponassembly, the heat sink segments 224 collectively constitute an innerenclosure 238 that extends around and surrounds the etalon mount 222,the latter of which incorporates a flange 240 that abuts a set of firstfaces 242 on one side of the heat sink segments 224, and is fastenedthereto with a plurality of fasteners 244, e.g. cap screws. The innerenclosure 238 is surrounded by an outer enclosure 246 comprising aplurality, e.g. three, heat-conducting outer ring segments 248, e.g.constructed on aluminum, each of which incorporates an inside face 250with an associated recess 252 that is adapted to receive and abut asecond surface 254 of the thermo-electric heat pump 236. Each of theouter ring segments 248 incorporate associated flanges 256 at both ends,one side 258 of which are adapted to cooperate with internal grooves 260in an outer shell 262 of the thermally-controlled enclosure 214, theother side 264 of which are adapted to cooperate with an outer ringretainer wedge 266 that operates between corresponding sides 264 ofadjacent flanges 256 of adjacent outer ring segments 248 when the outerring segments 248 are assembled to form the outer enclosure 246surrounding the inner enclosure 238.

The inner 238 and outer 246 enclosures are assembled together to form acore assembly 268, as follows. The solid optical element 116 Fabry-Pérotetalon 90 is bonded inside a bore 270 of the etalon mount 222 with athermal epoxy which provides for thermal conduction therebetween,wherein the inside diameter of the bore 270 is adapted so as to providefor a non-interfering fit with the solid optical element 116. The flange240 of the etalon mount 222 is attached with fasteners 244 to the firstfaces 242 of the three heat sink segments 224 assembled around theoutside surface 228 of the etalon mount 222. Three thermo-electric heatpumps 236 are sandwiched between respective recesses 232, 252 in acorresponding outer face 230 of each heat sink segment 224 and acorresponding inside face 250 of each outer ring segment 248, so thatthe first 234 and second 254 surfaces of the thermo-electric heat pumps236 abut and are in thermal communication with the correspondingassociated heat sink segment 224 and outer ring segment 248respectively. The core assembly 268 further comprises a plurality, e.g.three, temperature sensors 216, e.g. thermistors, resistive temperaturedevices, or thermocouples—each of which is inserted in a correspondinghole 272 in a second face 274 of each heat sink segment 224, so as toprovide for monitoring the temperature thereof, and so as to provide incooperation with the associated temperature controller 218 and theassociated thermo-electric heat pump 236, for controlling thetemperature thereof.

The core assembly 268 is inserted in the outer shell 262 so that theflanges 240 of the outer ring segments 248 mate with the correspondinginternal grooves 260 of the outer shell 262, and the outer ring retainerwedges 266 are inserted in the gaps 276 between the facing sides 264 ofthe flanges 240 so as to wedge the opposing sides 258 of the flanges 240against associated internal grooves 260 of the outer shell 262, therebyproviding for retaining the core assembly 268 within the outer shell262, and providing for thermal communication therebetween. The ends 278of the outer shell 262 are closed with associated end cap assemblies 280secured thereto with associated fasteners 282 and sealed therewithassociated seals 284, e.g. gaskets or o-rings. The end cap assemblies280 incorporate associated window assemblies 286 fastened thereto andincorporating optical windows 288, e.g. constructed from UV-grade fusedsilica substrates with standard anti-reflection coatings, which providefor transmission of the associated light signals 88. The resultingassembly constitutes a thermally-stabilized etalon assembly 290incorporating a thermally-controlled enclosure 214. Thethermally-stabilized etalon assembly 290 further comprises a pluralityof electrical connectors 292 therein which provide for connecting thethermo-electric heat pumps 236 and the temperature sensors 216 with theassociated temperature controller 218. The temperature controller 218uses the temperature sensors 216 to monitor the temperature of the coreassembly 268, and controls the heating or cooling thereof relative tothe environment using the associated thermo-electric heat pumps 236 soas to maintain the temperature of the core assembly 268 at a specifiedset-point. The outer enclosure 246 in thermal communication with theouter shell 262 provides for either supplying heat to or rejecting heatfrom the inner enclosure 238 responsive to the thermal effort of thethermo-electric heat pumps 236 as needed to maintain a particularset-point temperature. For example, in one embodiment, the set-pointtemperature is adapted so as to minimize the energy needed to maintainthat temperature, while also maintaining a sufficient offset so as tooperate the thermo-electric heat pumps 236 most efficiently. Forexample, for a thermo-electric heat pump 236 that operates mostefficiently when heating, the set-point temperature might be 5 to 10degrees Celsius above the nominal environmental temperature, e.g. 5 to10 degrees Celsius above room temperature.

In one embodiment, the firing of the Nd:YAG laser 12.1 is, for example,controlled with an associated Q-switch, which may be synchronized withthe acquisition of associated images 200 from the detector 164 using asynchronizer 294, thereby precluding the need for an electronic shutterthat would otherwise provide for gating light signals 88 to thedetector, although, alternatively, an electronic shutter could also beused or could be used without a synchronizer 294, for example, so as topreclude subsequent imaging during the process of reading image datafrom a CCD detector 164.1. The synchronizer 294, if used, could beincorporated in a control electronics assembly 296, e.g. which couldalso incorporate the associated temperature controller 218 and/or theassociated data processor 198. The synchronizer 294 could be adapted toeither generate a master timing signal for controlling both the laser 12and the detector 164, or could be adapted to relay a timing pulsegenerated by either one of the laser 12 and detector 164 to the other ofthe detector 164 and laser 12.

Referring to FIGS. 25-28, in accordance with several other embodiments,the optical air data system 10 comprises a laser 12 that generates afirst laser beam 14 which is divided into a reference beam 16 and asecond laser beam 18 by a first beam splitter 20.1. The second laserbeam 18 is directed into an optical head 22 incorporating associatedbeam steering optics 210 which divide the second laser beam 18 into aplurality of second laser beams 18.1, 18.2 and 18.3, each directed in adifferent direction, e.g. line of sight 40.1, 40.2, 40.3, into theatmosphere 24. For example, the beam steering optics 210 comprise second20.2 and third 20.3 beam splitters, wherein the second beam splitter20.2 reflects the first portion 18.1, e.g. about one third, of thesecond laser beam 18, and transmits a fourth portion 18.4, e.g. abouttwo thirds, thereof, and the third beam splitter 20.3 transmits thesecond portion 18.2, e.g. about one half, of the fourth portion 18.4 ofthe second laser beam 18, and reflects the remaining third portion 18.3of the second laser beam 18. The first portion 18.1 of the second laserbeam 18 reflected from the second beam splitter 20.2 is directed along afirst line of sight 40.1 by a first mirror 298, e.g. a front-surfacemirror, the second portion 18.2 of the second laser beam 18 istransmitted through the third beam splitter 20.3 along a second line ofsight 40.2, and the third portion 18.3 of the second laser beam 18reflected from the third beam splitter 20.3 is directed along a thirdline of sight 40.3 by a second mirror 300, e.g. a front-surface mirror.For example, the associated front-surface first 298 and second 300mirrors may each incorporate dielectric or metallic coatings (e.g.silver), or may comprise a long-wave-pass dichroic beam splitter. Theoptical head 22 further incorporates a plurality of respectivetelescopes 26.1, 26.2 and 26.3 each associated with a different of therespective second laser beams 18.1, 18.2 and 18.3 directed along or incooperation with respective lines of sight 40.1, 40.2 and 40.3, eachaimed at an associated respective interaction region 30.1, 30.2, 30.3 ofthe respective second laser beams 18.1, 18.2 and 18.3 projected into theatmosphere 24, and each adapted to collect the associated backscatteredlight signals 44 from each of the respective interaction regions 30.1,30.2, 30.3.

Each telescope 26 comprises a lens system 74, and the light signal 44collected thereby is collected by the final light-collecting element 72thereof into a corresponding fiber optic 76.2, 76.3, 76.4 that directsthe returned photons to associated portions of a Fabry-Pérotinterferometer 78 and an associated detection system 80 for processingthereby. The reference beam 16 from the laser 12 and beam splitter optic20 is separately collected by a separate light-collecting element 302into a fiber optic 76.1 directed to a separate portion of theFabry-Pérot interferometer 78 and an associated detection system 80 forsimultaneous processing thereby. For example, the final light-collectingelements 72 of the telescopes 26.1, 26.2 and 26.3, and thelight-collecting element 302 for collecting the reference beam 16, maycomprise either a GRIN lens or an aspheric lens. In one embodiment, theassociated fibers of the four fiber optics 76.1, 76.2, 76.3 and 76.4 arebundled together in a fiber-optic bundle 76′ which operatively couplesthe laser 12 and optical head 22 to the Fabry-Pérot interferometer 78.The use of fiber optics 76.1, 76.2, 76.3 and 76.4 and/or a fiber-opticbundle 76′ provides for simplifying the alignment of the Fabry-Pérotinterferometer 78 with the telescopes 26.1, 26.2 and 26.3 and with thereference beam 16 from the laser 12. Furthermore a separate fiber optic304 may be used to operatively couple the laser 12 to the optical head22, either directly from the output of the laser 12 to the optical head22—the latter of which could be adapted in an alternate embodiment of anoptical head 22′ to incorporate the first beam splitter 20.1,—or fromthe first beam splitter 20.1 to the optical head 22, or both, so as toprovide for flexibility in packaging the optical head 22 in relation tothe laser 12, which can be particularly beneficial for aircraftinstallations for which the optical head 22 is installed proximate tothe surface 36 of the aircraft 38, so as to provide for mounting thelaser 12 in a more benign and stable environment within the aircraft 38.A fiber optic 304 interconnecting the laser 12 with the optical head 22also provides for precise alignment of the associated first laser beam14 with the optical head 22, and simplifies associated installation andmaintenance of the associated components thereof.

The associated fiber optics 76.1, 76.2, 76.3, 76.4 and 304 can beadapted as necessary to incorporate non-solarizing fibers so as tomitigate against degradation from relatively high-energy UV laser lightwhich might otherwise solarize the associated fibers and thereby degradeassociated fiber-optic transmission. Furthermore, the fiber optic 304from the laser 12 to the optical head 22 may comprise a bundle ofassociated fibers, each adapted to transmit a portion of the total lightto be transmitted to the optical head 22, so as to reduce the energydensity within each fiber of the bundle and thereby mitigate against thedegradation thereof. For example, a beam expander may be used to enlargethe first laser beam 14 so as to distribute the associated energythereof amongst the plurality of associated fibers.

The light signals 44 collected by each of the telescopes 26.1, 26.2 and26.3, and the reference beam 16, are transmitted to the Fabry-Pérotinterferometer 78 by the associated fiber optics 76.1, 76.2, 76.3 and76.4 and are each simultaneously processed by a separate portion of aFabry-Pérot interferometer 78, wherein the light signals 44 andreference beam 16 passing through the Fabry-Pérot interferometer 78 arearranged with respect to one another in “cloverleaf” pattern, asillustrated in FIG. 26. The light signals 44 and reference beam 16 areeach collimated by a collimating lens 82, then filtered by a filtersystem 84 as described hereinabove, and then processed by the associatedFabry-Pérot etalon 90, the output of which is imaged by associatedimaging optics 100 as associated circular fringe patterns 106.1, 106.2,106.3 and 106.4 either directly onto a detector 164 as illustrated inFIG. 27, or into a quad-CLIO 126 which, as illustrated in FIG. 28,transforms the circular fringe pattern 106.1, 106.2, 106.3 and 106.4into a cross pattern 130 which is then imaged onto the detector 164. Theimage 200 from the detector 164 is then processed by a data processor198 which provides for determining the associated air data productstherefrom. The Fabry-Pérot interferometer 78 and the associateddetection system 80 may be mounted within a common housing 306.

The optical air data system 10 provides for directly detecting laserenergy scattered off of either molecules of the atmosphere, aerosols inthe atmosphere, or a combination of the two, provides for directlymeasuring the associated velocity and direction, density, andtemperature of the atmosphere, and provides for deriving an associatedcomplete set of air data products. For example, relatively shortwavelength laser energy is scattered by molecules of the atmosphere inaccordance with Rayleigh scattering. Laser energy can also be scatteredby aerosols in the atmosphere in accordance with Mie scattering.Rayleigh scattering generally refers to the scattering of light byeither molecules or particles having a size less than about 1/10^(th)the wavelength of the light, whereas Mie scattering generally refers toscattering of light by particles greater than 1/10^(th) the wavelengthof the light. Being responsive to Rayleigh scattering, the optical airdata system 10 is therefore responsive to the properties—e.g. velocity,density and temperature—of those molecules in the atmosphere giving riseto the associated scattering of the light detected by the optical airdata system 10. Accordingly, the optical air data system 10 provides foroperation in clean air, i.e. in an atmosphere with no more than anegligible amount of aerosols, depending substantially only uponmolecular backscatter.

The signals from the associated signal channels 122.1, 122.2 or 122.3received from any one of the three interaction regions 30.1, 30.2, 30.3are processed by the Fabry-Pérot interferometer 78 and acquired by theassociated one or more detectors 164. The reference channel 120 issimultaneously processed by the same Fabry-Pérot interferometer 78, andused to provide for calibrating measurements from each of theinteraction regions 30.1, 30.2, 30.3 associated with each of the fieldsof view 32 of each of the telescopes 26. The optical air data system 10uses the Fabry-Pérot interferometer 78 to directly detect informationfrom the scattered laser energy, wherein the reference 120 and signal122.1, 122.2, 122.3 channels are each detected separately, andinformation from the reference channel 120 can then be used to calibratethe associated signal channels 122.1, 122.2, 122.3. The detectionprocess is responsive to an incoherent Doppler shift of the laser lightbackscattered by molecules and aerosols in the atmosphere 24 responsiveto Rayleigh and Mie scattering respectively.

The optical air data system 10 can take advantage of aerosols whenpresent, but does not rely upon their presence. The signals from thereference channel 120 and the signal channels 122.1, 122.2 and 122.3 ofthe optical air data system 10 can be used to directly measure velocity,true airspeed, vertical speed, angle of attack, angle of sideslip,static density, static temperature, and aerosol to total scatteringratio (ASR). From these data products the following quantities can bedirectly calculated: calibrated airspeed, Mach number, static pressure,total pressure, dynamic pressure, pressure altitude, air density ratio,total temperature, angle of attack, pressure differential, andangle-of-sideslip pressure differential.

Wind velocity, density, and temperature are directly calculated usingthe fringe data from the Fabry-Pérot interferometer 78. The other airdata products are derived from these three basic measurements, in viewof the knowledge of the associated geometry of the optical head 22.Referring to FIG. 29, a first fringe 308 corresponds to a zero-wind,i.e. zero-velocity condition, and a second fringe 310 corresponds to anon-zero wind condition, wherein both the first 308 and second 310fringes are illustrated as exhibiting both an aerosol signal component308.1, 310.1 and a molecular signal component 308.2, 310.2 respectively.The reference channel 120 also provides for a zero wind condition, butdoes not contain either molecular or background components, andaccordingly would exhibit only the aerosol signal component 308.1illustrated in FIG. 29.

Referring to FIG. 30, the image 200 of the fringe pattern 92 generatedby the optical air data system 10 is modeled use non-linear least squaretechniques. The distribution of the stray light and background radiationis provided by measurements of the fringe pattern 92 with the laserseeder 208 turned off so as to enable the Nd:YAG laser 12.1 to lase overa relatively wider range of wavelengths that provides for simulatingbackground radiation. The fringe patterns 92 are otherwise measured withthe laser seeder 208 turned on so as to provide for substantiallysingle-frequency operation. The instrument functions and derivativesused in the algorithm are formed from analytic representations of theFabry-Pérot interferometer 78 and include the necessary broadeningfunctions to account for defects of the Fabry-Pérot etalon 90, e.g. theassociated solid optical element 116, as well as temperature-dependentline shape broadening from molecular backscatter. Empirical data for theillumination pattern is also used so that the correct light distributionof the fringes is accurately represented in the models. In an opticalair data system 10 with three signal channels 122.1, 122.2 and 122.3 forthree corresponding fields of view 32, and a reference channel 120, aline-of-sight relative wind velocity U is determined for each signalchannel 122.1, 122.2 and 122.3, which is calibrated using acorresponding measurement of the reference channel 120. As used herein,the term relative wind is intended to refer to the relative motionbetween the atmosphere—included molecules and aerosols—and the opticalair data system 10. In addition to frequency—which, responsive toassociated Doppler shift, provides for measuring associated velocity—thealgorithm determines the contribution to the fringe pattern frommolecular and aerosol backscatter, the background radiation, and thetemperature of the atmosphere 24 for each particular associated line ofsight 40.1, 40.2 and 40.3 along a direction of the correspondingassociated field of view 32 of the associated telescope 26.1, 26.2 and26.3. The molecular signal yields a measure of air density that can berelated to pressure. The aerosol to total scattering ratio is alsodirectly derived from the results.

The spectral shape of the light signal 44 of a signal channel 122.1,122.2 or 122.3 processed by the Fabry-Pérot etalon 90, for a singleassociated fringe to be modeled, has a qualitative form illustrated inFIG. 31, wherein the molecular scattered light, i.e. the molecularcomponent 310.2, exhibits a broadened spectral shape, while the aerosolscattered light, i.e. the aerosol component 310.1, produces a sharp peakwhich is nearly identical to the shape of the transmitted laser light.Underlying these two components is a background signal from scatteredsunlight, which at the scale of FIG. 31 forms a relatively flatcontinuum. By way of comparison, the corresponding spectral shape of thelight of the reference channel 120 processed by the Fabry-Pérot etalon90 is substantially the same as that of the aerosol component 310.1.

The transmission, T, of a perfect Fabry-Pérot etalon 90 is given by theAiry function as follows, and as described in Hernandez, G., Fabry-Perotinterferometers, Cambridge: Cambridge University Press, 1986, andVaughan, J. M., The Fabry-Perot Interferometer: History, Theory,Practice and Applications, Bristol, England: A. Hilger, 1989, both ofwhich documents are incorporated herein by reference:

$\begin{matrix}{{T(M)} = \frac{\left( {1 - \frac{L}{1 - R}} \right)^{2}\left( {1 - R} \right)^{2}}{1 - {2R\;\cos\; 2\pi\; M} + R}} & (6)\end{matrix}$where L is the loss per plate (absorption and scattering), R is theplate reflectivity, and M is the order of interference. Equation (6)describes a periodic transmission function, which is illustrated in FIG.32. The separation between peaks is known as the free spectral range anddepends inversely on the gap 98, 98.1 between the first 94 and second 96partially-reflective surfaces, so that a relatively large spacingresults in a relatively small free spectral range. The resolution of aFabry-Pérot interferometer 78 is determined by the full width at halfheight (FWHH) of a fringe, which in turn determines the Rayleighresolving power of the Fabry-Pérot interferometer 78. The finesse of theFabry-Pérot interferometer 78 is a unitless quantity that is defined asthe ratio of the Free Spectral Range(FSR) to the FWHH. Finesse definesthe number of resolvable elements that can fit in between two resonancepeaks, and represents the sensitivity of the Fabry-Pérot interferometer78. In the absence of any defects, the finesse is related primarily tothe reflectivity. For example, a reflectivity of 0.80 gives a finesse of14, and a reflectivity of 0.90 gives a finesse of 30. In the presence ofdefects, both the finesse and the peak transmittance are reduced. Unlesscareful attention is given to defects when a Fabry-Pérot system isdesigned, the finesse and throughput can be substantially less thananticipated and can adversely bias the measured results. In order toincorporate defects into the instrument model Equation (6) can bewritten in the equivalent series form, as follows:

$\begin{matrix}{{T(M)} = {\left( {1 - \frac{L}{1 - R}} \right)^{2}\left( \frac{1 - R}{1 + R} \right)\left( {1 + {2{\sum\limits_{n = 1}^{\infty}{R^{n}\cos\; 2\pi\;{nM}}}}} \right)}} & (7)\end{matrix}$Equation (7) is a useful form of the Airy function since it provides forrelatively easy convolutions with broadening functions.

The order of interference M is given by:M=2μtν cos θ  (8)where μ is the index of refraction of the material between the first 94and second 96 partially-reflective surfaces, t is the effective gap 98,98.1, ν is the wavenumber of light, and θ is the angle of incidence inthe Fabry-Pérot etalon 90 which is responsive to the focal length of theimaging optics 100 and the size of the detector 164. Perturbations of t,ν and θ from a set of standard conditions and normal incidence, can bemodeled as follows:

$\begin{matrix}{t = {t_{0} + {\Delta\; t}}} & (9) \\{v = {v_{0} + {\Delta\; v}}} & (10) \\{{\cos\;\theta} = {1 - \frac{\theta^{2}}{2}}} & (11)\end{matrix}$

The order of interference can then be written as follows:

$\begin{matrix}{M = {{2\mu\; t_{0}v_{0}} + {2\mu\; t_{0}\Delta\; v} + {2\mu\; v_{0}\Delta\; t} - {2\mu\; t_{0}v_{0}\frac{\theta^{2}}{2}}}} & (12)\end{matrix}$where only the first order terms have been retained, and can be furtherexpressed as follows:

$\begin{matrix}{M = {M_{o} + {\Delta\; M\mspace{14mu}{where}}}} & (13) \\{M_{0} = {2\mu\; t_{0}v_{0}\mspace{14mu}{and}}} & (14) \\{{\Delta\; M} = {{2\mu\; t_{0}\Delta\; v} + {2\mu\; v_{0}\Delta\; t} - {2\mu\; t_{0}v_{0}\frac{\theta^{2}}{2}}}} & (15)\end{matrix}$

The quantity ½ μt₀ is the change in wavenumber required to change theorder of interference by one, and is defined as the free spectral range,Δν_(FSR), which results in:

$\begin{matrix}{{\Delta\; M} = {\frac{\Delta\; v}{\Delta\; v_{FSR}} - {\frac{v_{0}}{\Delta\; v_{FSR}}\frac{\theta^{2}}{2}} + {2\mu\; v_{0}\Delta\; t}}} & (16)\end{matrix}$

Without loss of generality M₀ can be an integer and thereforeT(M)=T(ΔM).

Real instruments have defects which influence the behavior thereof andcan be accounted for by broadening functions in the models used tocharacterize the device. These broadening functions are well known andare represented by a set of probability functions which can be convolvedwith the basic Fabry-Pérot Airy function to give the general result:

$\begin{matrix}{{T\left( {{\Delta\; v},\theta} \right)} = {\left( {1 - \frac{L}{1 - R}} \right)^{2}{\left( \frac{1 - R}{1 + R} \right)\left\lbrack {1 + {2{\sum\limits_{n = 1}^{\infty}{R^{n}D_{n}\cos\; 2\;\pi\;{n\left( {\frac{\Delta\; v}{\Delta\; v_{FSR}} - {\frac{v_{0}}{\Delta\; v_{FSR}}\frac{\theta^{2}}{2}}} \right)}}}}} \right\rbrack}}} & (17)\end{matrix}$wherein the broadening function D_(n) filters the transmission Tdepending upon the magnitude of the defect or broadening process, and iscalculated from the following product:

$\begin{matrix}{D_{n} = {\prod\limits_{q = 1}^{N_{q}}d_{n}^{q}}} & (18)\end{matrix}$wherein d_(n) ^(q) is the n^(th) element of the convolution of theq^(th) broadening function G_(q)—described hereinbelow—with theinstrument model of Equation (7). The convolution integral is defined asfollows:

$\begin{matrix}{d_{n}^{q} = {\int_{- \infty}^{\infty}{{G_{q}\left( \delta^{\prime} \right)}*{T\left( {{M(n)} - \delta^{\prime}} \right)}{\mathbb{d}\delta^{\prime}}}}} & (19)\end{matrix}$where T(M(n)−δ′) is the Fabry-Perot infinite series term.

A simplified notation can be used to provide for a more compactrepresentation, wherein

$\begin{matrix}\begin{matrix}{A_{n} = {{\left( {1 - \frac{L}{1 - R}} \right)^{2}\left( \frac{1 - R}{1 + R} \right)\mspace{14mu}{for}\mspace{14mu} n} = 0}} \\{= {{2\left( {1 - \frac{L}{1 - R}} \right)^{2}\left( \frac{1 - R}{1 + R} \right)\; R^{n}D_{n}\mspace{14mu}{for}\mspace{14mu} n} > 0}}\end{matrix} & (20)\end{matrix}$so that the Airy function can be written as follows:

$\begin{matrix}{{T\left( {{\Delta\; v},\theta} \right)} = {\sum\limits_{n = 0}^{\infty}{A_{n}\cos\; 2\;\pi\;{n\left( {\frac{\Delta\; v}{\Delta\; v_{FSR}} - {\frac{v_{0}}{\Delta\; v_{FSR}}\frac{\theta^{2}}{2}}} \right)}}}} & (21)\end{matrix}$

The broadening functions G_(q) account for broadening resulting fromeach of Doppler shift, laser width, scattering broadening, and turbulentmotion, respectively, as given hereinbelow, for N_(q)=3 in Equation(18).

Doppler Broadening: The Doppler shift due to the mean air motion isgiven by:

$\begin{matrix}{{\Delta\; v} = {v_{1}\frac{2U_{h}\sin\;\phi}{c}}} & (22)\end{matrix}$where Δν is the Doppler shift, ν₁ is the laser wavenumber, U_(h) is thehorizontal wind speed in the direction of viewing, and φ is the anglefrom the zenith made by the second laser beams 18.1, 18.2 or 18.3 as itpasses through the atmosphere 24, wherein U_(h) sin φ is theline-of-sight relative wind velocity U. Accordingly, Equation (22)provides the relationship between line-of-sight relative wind velocity Uand the Doppler shift Δν.

Laser Spectral Width Broadening: The spectral shape of the laser isassumed to be of Gaussian form, as follows:

$\begin{matrix}{{G_{laser}\left( {{\Delta\; v},{\Delta\; v_{1}}} \right)} = {\frac{1}{\sqrt{\pi}\Delta\; v_{1}}{\mathbb{e}}^{- \frac{\Delta\; v^{2}}{\Delta\; v_{1}^{2}}}}} & (23)\end{matrix}$where Δν₁ is the 1/e width of the laser, wherein the shorter theduration a laser pulse, the broader the associated broadening function,which results in lowered finesse for the Fabry-Pérot etalon 90.

Scattering Broadening: The affect on the transmission T of a Fabry-Pérotinterferometer 78 due to broadening induced by molecular scattering isdifferent from that induced by aerosol scattering. Accordingly,different broadening functions G_(q) are used to account for molecularand aerosol scattering, respectively, in respective corresponding modelsfor the molecular T_(Mol) and aerosol T_(Aero) components oftransmission T of the Fabry-Pérot interferometer 78.

The molecular scattering media broadens the signal due to associatedrandom motions. The molecules have a Gaussian broadening function, asfollows:

$\begin{matrix}{{G_{molecules}\left( {{\Delta\; v},{\Delta\; v_{G}}} \right)} = {\frac{1}{\sqrt{\pi}\Delta\; v_{G}}{\mathbb{e}}^{- \frac{\Delta\; v^{2}}{\Delta\; v_{G}^{2}}}}} & (24)\end{matrix}$where Δν_(G) is the 1/e width and is given by:

$\begin{matrix}{{{\Delta\; v_{G}} = {\frac{v_{l}}{c}\left( \frac{2{k \cdot {Temp}}}{m} \right)^{\frac{1}{2}}}}{or}} & (25) \\{{\Delta\; v_{G}} = {4.30 \times 10^{- 7}{v_{l}\left( \frac{Temp}{\overset{\_}{M}} \right)}^{\frac{1}{2}}}} & (26)\end{matrix}$where k is Boltzmann's constant, m is the mean mass of a molecule in theatmosphere, Temp is the static absolute temperature in degrees Kelvin,and M is the mean molecular weight ( M=28.964).

The aerosol broadening function has a Lorentzian form as follows, forexample, as described in Fiocco, G., and DeWolf, J. B., “Frequencyspectrum of laser echoes from atmospheric constituents and determinationof aerosol content of air,” Journal of Atmospheric Sciences, v.25, n3,May 1968, pp. 488-496; and Benedetti-Michelangeli, G., Congeduti, F.,and Fiocco, G., “Measurement of aerosol motion and wind velocity in thelower troposphere by Doppler optical radar,” Journal of the AtmosphericSciences, v.29, n5, July 1972, pp. 906-910, both of which references areincorporated herein by reference:

$\begin{matrix}{{L_{aerosol}\left( {{\Delta\; v},\alpha_{A}} \right)} = {\frac{1}{\pi}\frac{\alpha_{A}}{\alpha_{A}^{2} + {\Delta\; v^{2}}}}} & (27)\end{matrix}$where the half width α_(A) is given by:

$\begin{matrix}{\alpha_{A} = \frac{2\pi\; v^{2}D}{c}} & (28)\end{matrix}$The spectral width of the aerosol-induced broadening component isextremely narrow compared to the molecular-induced broadening component,and in most cases are much narrower than the laser pulse, so thataerosol scattering essentially acts as a delta function and is notdependent on temperature.

Turbulent Motion Broadening: In addition to random motions of moleculesand aerosols, the model allows for random motions of bulk parcels, i.e.turbulence, wherein this broadening is represented by a relativelysimple Gaussian shape, as follows:

$\begin{matrix}{{G_{turbulence} = {\left( {{\Delta\; v},{\Delta\; v_{T}}} \right) = {\frac{1}{\sqrt{\pi}\Delta\; v_{T}}{\mathbb{e}}^{- \frac{\Delta\; v^{2}}{\Delta\; v_{T}^{2}}}}}},{where}} & (29) \\{{{\Delta\; v_{T}} = {\frac{v_{1}}{c}U_{T}}},} & (30)\end{matrix}$and U_(T) is a characteristic turbulent velocity, which is a predefinedconstant that is independent of the line-of-sight relative wind velocityU. In some embodiments, this term is ignored because it isindistinguishable from temperature, so that the affects of Equations(24) and (29) are indistinguishable from one another.

Other broadening functions G_(q) can also be utilized in addition tothose described hereinabove, for example, so as to account for a defocusof the imaging optics 100.

The values of the line of binned pixels 188.1, 188.2, 188.3 and 188.4for the reference 120 and signal 122.1, 122.2, 122.3 channels,respectively, provide a corresponding transmission measure T′ of theFabry-Pérot interferometer 78 for the corresponding reference 120 andsignal 122.1, 122.2, 122.3 channels, respectively. Each transmissionmeasure T′ is an N-element vector, wherein each element n of the vectorcorresponds to a different wavelength or corresponding order ofinterference. The element values are in units of measurement counts; forexample, with one measurement count being equal to one photo-electroncaptured by the detector 164. The transmission measure T′ is a measureof data from the Fabry-Pérot interferometer 78 that can be modeled asdescribed hereinabove in accordance with Equations (6) through (30), asrepresented by FIGS. 31 and 32, wherein FIG. 31 illustrates a finerscale of detail of each fringe illustrated in FIG. 32. Accordingly, thetransmission measure T′, in units of total counts of binned values fromthe detector 164, can be modeled as the sum of associated molecular,aerosol and background counts, as follows:T=T _(Mol)(Temp,U)·MolCounts+T _(Aero)(U)·AeroCounts+T_(Back)·BackCounts  (31)where T_(Mol)(Temp,U)·MolCounts is the component of transmission T ofthe Fabry-Pérot interferometer 78 resulting from molecular backscatter,which is a function of temperature and line-of-sight relative windvelocity U; T_(Aero)(U)·AeroCounts is the component of transmission T ofthe Fabry-Pérot interferometer 78 resulting from aerosol backscatter,which is not affected by temperature but is dependent upon theline-of-sight relative wind velocity U; and T_(Back)·BackCounts is thecomponent of transmission T of the Fabry-Pérot interferometer 78resulting from stray light and background wherein T_(Back) is thecontinuum distribution or illumination profile through the instrumentthat is measured during calibration of the instrument from the responseof the Fabry-Pérot interferometer 78 with the laser seeder 208 turnedoff, which is representative of the associated spectral distributionfrom the Fabry-Pérot interferometer 78 that would result from backgroundillumination. During operation of the optical air data system 10, thecontinuum distribution T_(Back) is obtained from pre-measured valuesthat are stored in memory, and the components T_(Mol) and T_(Aero) arecalculated from Equation (21) using the appropriate associatedbroadening terms. Each of the above-described components of transmissionT of the Fabry-Pérot interferometer 78 is in units of counts resultingfrom the charge collected by the elements of the detector 164. Thedistributions T_(Mol)(Temp,U), T_(Aero)(U) are evaluated with Equation(21) using broadening functions that are appropriate for the molecularand aerosol components of backscatter, respectively. In practice, whenevaluating Equation (21), the associated infinite series is truncated toignore higher-order terms of relatively insignificant value, wherein thelevel of truncation is either predetermined, or determined during theaccumulation of the elements of the series.

Accordingly, the transmission T of the Fabry-Pérot interferometer 78 ismodeled with a non-linear model of Equation (31) that is parameterizedby a first set (or vector) of parameters P that characterize aparticular measurement, i.e. which characterize a particulartransmission measure T′; and a second set of parameters Q which areassumed constant during operation of the Fabry-Pérot interferometer 78,the values of which are determined during calibration. Referring to FIG.30, the first set of parameters P, referred to as observables, includethe following elements: line-of-sight relative wind velocity U, statictemperature Temp, molecular counts MolCounts, aerosol counts AeroCounts,and backscatter counts BackCounts. The second set of parameters Qincludes the gap 98, 98.1 (t), index of refraction μ (1 for an air gap)and reflectivity R of the Fabry-Pérot etalon 90, the nominal wavenumberν (or wavelength λ) of the light 28 from the laser 12, the focalproperties of the imaging optics 100 (i.e. θ in Equation (8)), and thecontinuum distribution T_(Back).

The observables P can be determined as the values of the parameters Pthat minimize the following χ² merit function:

$\begin{matrix}{{\chi^{2}\left( {P,Q} \right)} = {\sum\limits_{n = 1}^{N}\frac{\left\lbrack {{T^{\prime}(n)} - {T\left( {{{M(n)};P},Q} \right)}} \right\rbrack^{2}}{\sigma^{2}(n)}}} & (32)\end{matrix}$using, for example, a Levenberg-Marquardt method of a non-linear leastsquare process which provides for varying smoothly between aninverse-Hessian method and a steepest descent method, as described,along with other suitable non-linear methods, by W. H. Press, S. A.Teukolsky, W. T Veterling, and B. P. Flannery in Numerical Recipes in C,The Art of Scientific Computing, Second Edition, Cambridge UniversityPress, 1992, pp. 656-661 and 681-706 which is incorporated herein byreference. In Equation (32), T′(n) is the value of the n^(th) binnedpixel 190, and T(M(n),P,Q) is the value of the transmission model T fromEquation (31).

Accordingly, for the optical air data system 10, the transmission modelT is overdetermined in the sense that the number of elements N of thedetector 164, i.e. the number of binned pixels per channel, is of ahigher dimension than the number of observables P. For the optical airdata system 10 embodiment described herein, there are 5 observables P.

In the inverse Hessian method, the gradient of χ² is given by:

$\begin{matrix}\begin{matrix}{\beta_{k} = \frac{\partial\chi^{2}}{\partial P_{k}}} \\{= {{- 2}{\sum\limits_{n = 1}^{N}{\frac{\left\lbrack {{T^{\prime}(n)} - {T\left( {{{M(n)};P},Q} \right)}} \right\rbrack}{\sigma^{2}(n)}\frac{\partial{T\left( {{{M(n)};P},Q} \right)}}{\partial P_{k}}}}}}\end{matrix} & (33)\end{matrix}$and the Hessian is approximated by:

$\begin{matrix}{\alpha_{kl} = {\frac{\partial^{2}\chi^{2}}{{\partial P_{k}}{\partial P_{l}}} = {2{\sum\limits_{n = 1}^{N}{\frac{\partial{T\left( {{{M(n)};P},Q} \right)}}{\partial P_{k}}\frac{\partial{T\left( {{{M(n)};P},Q} \right)}}{\partial P_{l}}}}}}} & (34)\end{matrix}$where k=1 to 5 for the 5 observables.

The observables are then solved by solving the set of linear equations:

$\begin{matrix}{{\sum\limits_{l = 1}^{5}{\alpha_{kl}\delta\; P_{l}}} = \beta_{k}} & (35)\end{matrix}$where δP_(l) is an vector increment that is to be added to a currentapproximation for the observable vector P_(l). This system of equationscan be represented as:A·δP=B  (36)where A is the Hessian matrix, δP is a vector of increments to theobservables that are to be added to a current approximation for theobservable P, and B is the gradient vector. This system of equations canbe solved as follows:δP=A ¹ ·B  (37)where A⁻¹ is the inverse Hessian matrix.

The inverse Hessian method is suitable when the χ² merit function can belocally approximated by a quadratic form. If a quadratic form is arelatively poor local approximation, then the steepest descent formulacan be used to find the increment δP of the observable P as follows:δP _(l)=constant×β_(k)  (38)

The Levenberg-Marquardt method provides for a combination of the inverseHessian and steepest descent methods, wherein the Hessian matrix inEquation (35) is replaced with:α_(kk)′=α_(kk)·(1+λ)α_(jk)′=α_(jk) (j≠k)  (39)and both Equations (35) and (38) are replaced with the following:

$\begin{matrix}{{\sum\limits_{l = 1}^{5}{\alpha_{kl}^{\prime}\delta\; P_{l}}} = \beta_{k}} & (40)\end{matrix}$the solution of which is given by:δP=A′ ⁻¹ ·B  (41)where the elements of A′ are given by α′_(jk).

The Levenberg-Marquardt method commences with an initial guess for theobservable vector P, after which χ²(P,Q) is calculated, and an initialvalue of λ is chosen (e.g. λ=0.001). An iterative process then commenceswith the solution for δP of Equation (41), and the evaluation ofχ²(P+δP,Q). If χ²(P+δP,Q)≧χ²(P,Q), then λ is increased, e.g. by a factorof 10, and the iteration is repeated. Otherwise, if χ²(P+δP,Q)<χ²(P,Q),then λ is decreased, e.g. by a factor of 10, and the iteration isrepeated. The iterations on the observable vector P are continued untila stopping criteria is satisfied, for example, on the first or secondoccasion when χ² decreases by a negligible amount, and with the finalsolution, the method converses towards the inverse Hessian method.

The components of the gradient of the transmission model T used incalculating the gradient of χ² and the Hessian matrix are given asfollows, and are calculated numerically:

$\begin{matrix}{\frac{\partial{T\begin{pmatrix}{U,{MolCounts},} \\{{AeroCounts},} \\{{Temp},{BackCounts}}\end{pmatrix}}}{\partial U} = {\frac{\partial}{\partial U}\begin{pmatrix}{{T_{Mol}\left( {{Temp},U} \right)} \cdot} \\{{MolCounts} +} \\{{T_{Aero}(U)} \cdot {AeroCounts}}\end{pmatrix}}} & (42) \\{\frac{\partial{T\begin{pmatrix}{U,{MolCounts},{AeroCounts},} \\{{Temp},{BackCounts}}\end{pmatrix}}}{\partial{MolCounts}} = {T_{Mol}\left( {{Temp},U} \right)}} & (43) \\{\frac{\partial{T\begin{pmatrix}{U,{MolCounts},{AeroCounts},} \\{{Temp},{BackCounts}}\end{pmatrix}}}{\partial{AeroCounts}} = {T_{Aero}(U)}} & (44) \\{\frac{\partial{T\begin{pmatrix}{U,{MolCounts},{AeroCounts},} \\{{Temp},{BackCounts}}\end{pmatrix}}}{\partial{Temp}} = {\frac{\partial}{\partial{Temp}}{T_{Mol}\left( {{Temp},U} \right)}}} & (45) \\{\frac{\partial{T\begin{pmatrix}{U,{Mol},{Aero},} \\{{Temp},{BackCounts}}\end{pmatrix}}}{\partial{BackCounts}} = T_{Back}} & (46)\end{matrix}$

When processing the reference channel 120, the observables MolCounts andBackCounts are assumed to be zero valued, and the partial derivativeswith respect to MolCounts, BackCounts and Temp of Equations (43), (46)and (45), respectively, are also assumed to be zero.

The σ²(n) weighing term in the χ² merit function is the associatedvariance of the n^(th) measurement channel (i.e. interference order orwavelength), which includes variance of the collected signal incombination with the variance associated with the noise from thedetector 164. The collected photons exhibit Poisson noise statistics.Accordingly, for Signal(n) photons/counts/photo-electrons collected on asingle channel, the associated variance is equal to the signal level, asfollows:σ_(Signal) ²(n)=Signal(n)  (47)wherein the Signal(n) is the sum of the molecular, aerosol andbackground components, i.e.:Signal(n)=Molecular(n)+Aerosol(n)+Background(n)  (48)so that Signal(n) is the predicted value from Equation (31). The totalvariance is the combination of the signal variance and the variance ofthe detector, as follows:σ²(n)=Signal(n)+Noise_(Detector)(n)²  (49)wherein, for a CCD detector 164.1, the detector noise is the associatedread noise on each detector channel.

Alternatively, the observables P could be estimated using othernon-linear modeling or non-linear programming techniques, or othertechniques such as non-linear estimation or Kalman filtering.

Referring to FIGS. 29 and 33, in accordance with a first measurementprocess 3302, the relative wind velocity V₁, V₂ or V₃ is determinedalong a corresponding line-of-sight direction of the correspondingassociated field of view 32 of the associated telescope 26.1, 26.2 and26.3 for each line of sight 40.1, 40.2 or 40.3 from a difference betweenthe centroids of the associated circular fringe pattern 106.2, 106.3 or106.4 associated with a corresponding signal channel 122.1, 122.2 or122.3 in comparison with that of the circular fringe pattern 106.1associated with the reference channel 120. The fringe position relativeto the optic axis 112 directly related to wavelength. Accordingly, adifference in wavelength between the circular fringe patterns 106.2,106.3 or 106.4 associated with a signal channel 122.1, 122.2 or 122.3and circular fringe pattern 106.1 associated with the reference channel120 is a direct measure of the molecular/aerosol Doppler shift in thelight 28 that is backscattered from the atmosphere 24 responsive toeither molecular or aerosol scattering. The relative wind velocity V₁,V₂ or V₃ for each associated signal channel 122.1, 122.2 or 122.3 iscalculated by subtracting the associated line-of-sight velocity Uobservable solved by Equation (41) from the corresponding “line-of-sightvelocity U” observable of the reference channel 120, similarly sosolved, so as to provide an associated calibrated relative wind velocityV₁, V₂ or V₃.

Referring to FIGS. 29 and 33, in accordance with a second measurementprocess 3304, the air density, i.e. static density ρ, is determined froman integral of the molecular signal component 308.2, 310.2 of thecircular fringes 108.2, 108.3 or 108.4 associated with a signal channel122.1, 122.2 or 122.3. The density of the atmosphere 24 is related tomolecular density, not aerosol density. Accordingly, the Rayleighbackscatter is separated from the Mie backscatter by spectrallyresolving the backscattered light and de-convolving the spectrum intoassociated molecular and aerosol contributions, which provides fordetermining the density of the atmosphere 24 from the associatedmolecular component responsive to the total number of photons therein,i.e. responsive to an integral of the molecular signal component inaccordance with Rayleigh scattering theory. The denser the air is, themore molecules are present to scatter light 28 back to the telescope 26for detection by the associated detector 164. The observables MolCountsand AeroCounts resulting from the solution of the minimization ofEquation (32) inherently provides for a deconvolution of the spectruminto the associated molecular and aerosol contributions, i.e. MolCountsis responsive to the integral of the molecular contribution, andAeroCounts is responsive to the integral of the aerosol contribution.Accordingly, static density is given by ρ=C·MolCounts, wherein C is anempirically determined constant that depends upon the parameters thatdefine the optical air data system 10, i.e. the laser power, interactionregion, the transmission of the system, the gain of the detectors, thesize of the telescope, and the coefficient of backscatter from theatmospheric molecules.

Referring to FIGS. 29 and 33, in accordance with a third measurementprocess 3306, the absolute temperature, i.e. static temperature T_(S),of the atmosphere 24 is determined from a width of the molecular signalcomponent 308.2, 310.2 of the circular fringes 108.2, 108.3 or 108.4associated with a signal channel 122.1, 122.2 or 122.3. The temperatureof the atmosphere 24 affects the random thermal motions of theconstituent molecules, which causes an associated thermalbroadening—referred to as “Doppler broadening” in the field ofspectroscopy because of the random velocities in all directions of anensemble of molecules—of the spectrum of the associated scatteredradiation, thereby increasing the associated signal bandwidth whichproduces correspondingly wider fringes in the associated circular fringepatterns 106.2, 106.3 and 106.4 from the Fabry-Pérot interferometer 78.The absolute temperature of the atmosphere 24 is directly related tothis signal bandwidth, and is directly determined as the observable Tempresulting in the solution of the minimization of Equation (32).

Referring to FIG. 33, various other measured air data products may becalculated as follows: In accordance a fourth measurement process 3308,the relative wind velocities V₁, V₂ and V₃ determined by the firstmeasurement process 3302 along corresponding line-of-sight directions ofthe corresponding associated field of view 32 of the associatedtelescope 26.1, 26.2 and 26.3 for each lines of sight 40.1, 40.2 or 40.3are first transformed from a line-of-sight frame of reference to a frameof reference (x_(m), y_(m) and z_(m)) of the optical air data system 10,and then to a frame of reference (x, y, z) of the aircraft 38 usingknown transformations, so as to provide the relative wind velocitiesV_(X), V_(Y) and V_(Z) in the frame of reference (x, y, z) of theaircraft 38, from which the true airspeed V_(T) may be calculated fromthe relative wind velocities V_(X), V_(Y) and V_(Z) in accordance with afifth measurement process 3310. The vertical speed H′_(P) is given bythe Z-component of relative wind velocity V_(Z). The sideslip may becalculated from the Y-component of relative wind velocity V_(Y) and thetrue airspeed V_(T) in accordance with a sixth measurement process 3312.The angle of attack may be calculated from the X and Z-components ofrelative wind velocity V_(X) and V_(Z) in accordance with a seventhmeasurement process 3314. The Aerosol-to-Total Scattering Ratio (ASR)may also be calculated as the ratio of the observable AeroCounts to thesum of the observables MolCounts, AeroCounts and BackCounts. Referringto FIG. 34, the measured values of static density ρ, static temperatureT_(S), true airspeed V_(T), sideslip and angle of attack may then beused to compute the following derived values using associated knownrelations and processes: air density ratio, static pressure, totalpressure, pressure altitude, total temperature, speed of sound, Machnumber, dynamic pressure, calibrated airspeed, angle of sideslippressure differential, and angle of attack pressure differential.

Referring to FIGS. 3 and 4, the optical air data system 10, either withan optical head 22.1 incorporating a biaxial system 50 (also known as abistatic system) as illustrated in FIG. 3, or with an optical head 22.2incorporating a coaxial system 66 as illustrated in FIG. 4, may beadapted as either a non-ranging system or a ranging system. In thenon-ranging embodiment, the measurement volume consists of one regionthat spans the entire interaction region between the field of view 32 ofthe associated telescope 26.1, 26.2, 26.3 and the line of sight 40.1,40.2, 40.3 of the associated second laser beam 18.1, 18.2 and 18.3.

Accordingly, referring also to FIGS. 35-42, in accordance with anotheraspect, an optical air data system 10′, either with an optical head 22.1incorporating a biaxial system 50 or with an optical head 22.2incorporating a coaxial system 66 (also known as a monostatic system),may be adapted so as to provide for air data products as a function ofrange 46. In the ranging embodiment, a sufficiently fast CCD detector164.1 is responsive to the time of flight of each laser pulse, therebyproviding for multiple range-separated measurement volumes 311 extendingout along the line of sight 40.1, 40.2, 40.3 of the associated telescope26.1, 26.2, 26.3, so as to provide for mapping the air data products asthey vary along the line of sight 40.1, 40.2, 40.3 extending out fromthe optical head 22.1, 22.2, e.g. from an associated aircraft 38 forwhich the associated range-based air data products can be used byassociated flight guidance and planning algorithms.

Referring to FIGS. 35-40, the optical air data system 10′ incorporates abi-CLIO 312, for example, comprising a first pyramidal shaped opticelement 314 which cooperates with first 316.1 and second 316.2 cornerreflector optic elements, which in turn cooperate with a secondpyramidal shaped optic element 318. Two of the opposing side faces 320of the first pyramidal shaped optic element 314 incorporate associatedfirst 134.1 and second 134.2 concave conical reflectors adapted toreceive an associated circular fringe patterns 106.1 and 106.2, and106.3 and 106.4, respectively, from the Fabry-Pérot interferometer 78,wherein the associated fiber optics 76.1, 76.2, 76.3 and 76.4 inputtingto the Fabry-Pérot interferometer 78 are arranged substantially in-linewith a center of the first 314 and second 318 pyramidal shaped opticelements. The first concave conical reflector 134.1 is adapted toreceive a first two circular fringe patterns 106.1, 106.2, and thesecond concave conical reflector 134.2 is adapted to receive theremaining two circular fringe patterns 106.3 and 106.4.

Light signals 88 of the first two circular fringe patterns 106.1, 106.2are reflected from the first concave conical reflector 134.1 onto afirst reflective surface 322 of the corresponding first corner reflectoroptic element 316.1, and then reflected therefrom onto a secondreflective surface 324 of the corresponding first corner reflector opticelement 316.1, and then reflected therefrom onto a third reflectivesurface 326 on a first side face 328 of the second pyramidal shapedoptic element 318, and finally reflected therefrom onto a first portion330 an associated CCD detector 164.1 as corresponding first 332.1 andsecond 332.2 linear fringe patterns. Similarly, light signals 88 of theremaining two circular fringe patterns 106.3 and 106.4 are reflectedfrom the second concave conical reflector 134.2 onto a fourth reflectivesurface 334 of a corresponding second corner reflector optic element316.2, and then reflected therefrom onto a fifth reflective surface 336of the corresponding second corner reflector optic element 316.2, andthen reflected therefrom onto a sixth reflective surface 338 on a secondside face 340 of the second pyramidal shaped optic element 318, andfinally reflected therefrom onto a second portion 342 an associated CCDdetector 164.1 as corresponding third 332.3 and fourth 332.4 linearfringe patterns. For example, in one embodiment, the first 322, second324, third 326, fourth 334, fifth 336 and sixth 338 reflective surfacescomprise corresponding planar reflective surfaces 322′, 324′, 326′,334′, 336′, 338′. The first 314 and second 318 pyramidal shaped opticelements and the first 316.1 and second 316.2 corner reflector opticelements can be constructed from a variety of materials—including, butnot limited to, aluminum, stainless steel, copper-nickel alloy, glass orfused quartz—that can be adapted to incorporate associated reflectivesurfaces or coatings. Furthermore, one or both of the first 316.1 andsecond 316.2 corner reflector optic elements could be replaced withseparate elements for each of the associated first 322, second 324,fourth 334 and fifth 336 reflective surfaces.

Referring to FIGS. 40 and 41, the first 332.1, second 332.2, third 332.3and fourth 332.4 linear fringe patterns are projected onto theassociated first 330 and second 342 portions of the CCD detector 164.1located proximate to an associated serial register 344 thereof, and theremaining photosites 346 of the CCD detector 164.1 are masked fromreceiving light. The CCD detector 164.1 comprises an array 348 ofphotosites 346 organized as a plurality of rows 350, each row comprisinga plurality of columns 352. Upon exposure to light, each of thephotosites 346 accumulates charge in proportion to the amount of lightimpinging thereon. In a normal process of recording a 2-dimensionalimage, the entire array 348 is simultaneously exposed to an entireimage, e.g. by the opening of an associated shutter or by the activationof the laser 12 illumination source. Then, with the shutter closed orthe laser 12 off after the light signals 44 have been received, the2-dimensional image is read from the array 348, one row 350 at a time,by successively shifting the charges from each row 350 successivelydownwards, for example, by first shifting the charges from row #1 intothe serial register 344, then shifting the charges from row #2 into row#1, then row #3 into row #2, and so on until the charges from row #N isshifted into row #N−1. The contents of the serial register 344 are thenA/D converted and communicated to an associated processor for subsequentprocessing. Afterwards, this process repeats on rows #1 to #N−1, and soon until the last row 350 of recorded photosites 346 has beentransferred to the serial register 344, and then to the associatedprocessor for subsequent processing.

The optical air data system 10′ takes advantage of the normal process bywhich the CCD detector 164.1 is read to provide for continuouslyrecording the first 332.1, second 332.2, third 332.3 and fourth 332.4linear fringe patterns over time so that each subsequent row 350 ofphotosites 346 passing by first 330 and second 342 portions of the CCDdetector 164.1 during the process of reading the CCD detector 164.1captures the associated first 332.1, second 332.2, third 332.3 andfourth 332.4 linear fringe patterns at a corresponding subsequent pointin time with data associated with a corresponding range 46 from theoptical head 22.1, 22.2. More particularly, the process of reading theCCD detector 164.1 commences simultaneously with the generation of anassociated light pulse from the laser 12. Light signals 88 arecontinuously processed by the Fabry-Pérot interferometer 78 andassociated bi-CLIO 312 so as to illuminate the first 330 and second 342portions of the CCD detector 164.1 with corresponding first 332.1,second 332.2, third 332.3 and fourth 332.4 linear fringe patterns. Inthe CCD detector 164.1 illustrated in FIG. 40, the first 330 and second342 portions of the CCD detector 164.1 are aligned with row #2 thereof.After the charges from row #2 are transferred to row #1 during a chargetransfer cycle 354, row #2 is replaced with the blank contents of row#3, which then becomes exposed to the light signals 88 from the first332.1, second 332.2, third 332.3 and fourth 332.4 linear fringe patternsat that time. This process repeats with a fresh row of blank photosites346 replacing the contents of row #2 with each subsequent chargetransfer cycle 354 until all of the rows 350 have been read. During eachcharge transfer cycle 354, the contents of row #1 are shifted into theserial register 344, and then transferred to the data processor 198where the corresponding values are stored in memory 202 as pixels 180 ofan associated image 356, beginning from the bottom 358 of the image 356,and progressing upwards 360 until the entire image 356 has beenrecorded, as illustrated in FIG. 41, whereupon the image 356 recordseach of the first 332.1, second 332.2, third 332.3 and fourth 332.4linear fringe patterns in corresponding range-resolved fringe patterns362.1, 362.2, 362.3 and 362.4, with range 46 (R) increasing upwards 360in the associated image 356. The range resolution of the image 356 isdependent upon the time required for each charge transfer cycle 354,i.e. the time required to transfer the associated charges from one rowto the next. For example, for a CCD detector 164.1 with 512 rows and arow shift rate of 375 nanoseconds per row, the range resolution would be56.25 meters (i.e. 3.0×10⁸ m/s*½*375×10⁻⁹ s) and the maximum range forthe CCD detector 164.1 would be 28.8 Kilometers (i.e. 512*56.25). Theframe transfer/streaking process/range acquisition takes only arelatively short time, e.g. for 512 rows at a streak rate of 375 ns/rowit takes 192 micro-seconds to resolve the full range on the CCD detector164.1. For a 200 Hz refresh rate a frame is acquired every 5milliseconds ( 1/200), so there are 0.00500−0.000192=0.004808 secondsfor reading the image out of the readout registers and transferring todisk in accordance with an associated process of acquiring image framesfrom the CCD detector 164.1 at an associated refresh rate thereof, e.g.in frames per second.

Referring to FIG. 42, in accordance with a first imaging process 4200for generating a range-resolved image, for example, operative incooperation with the CCD detector 164.1 illustrated in FIG. 40 togenerate an associated image 356, e.g. as illustrated in FIG. 41, instep (4202), the array 348 of photosites 346 of the CCD detector 164.1is initialized, e.g. to substantially zero charge. Then, in step (4204),in synchronism with the lasing of the second laser beams 18 from thelaser 12, for a pulsed laser 12, an iteration count is initialized, e.g.to a value of zero, wherein the iteration count is used to record thenumber of times the array 348 of photosites 346 has been processed insubsequent steps. Then, in step (4206), a first row counter IRow isinitialized to a value of NRow, where NRow is the number of rows in thearray 348 of photosites 346; and a second row counter KRow isinitialized to a value of 1. Then, in step (4208), an iterative processcommences, wherein charge is accumulated in the photosites 346 in arecording zone 364 comprising the first 330 and second 342 portions ofthe CCD detector 164.1 that are aligned with a particular row of thearray 348 of photosites 346 and which receive light 28 of the first332.1, second 332.2, third 332.3 and fourth 332.4 linear fringe patternsfrom the associated fiber optics 76.1, 76.2, 76.3 and 76.4. Then, instep (4210), the charges in the photosites 346 of row #1 are shiftedinto a buffer row 366, and then, in step (4212), the charges in row ##2to IRow are shifted into row ##1 to IRow−1, respectively. Then, in step(4214), if the iteration count is less than a threshold, then in step(4216), the second row counter KRow is incremented, and, in step (4218),the charges in the buffer row 366 are shifted into Row #NRow. Then, instep (4220), if the value of the second row counter KRow is greater thanor equal to the number of rows NRow, then, in step (4222), the iterationcount is incremented and the second row counter KRow is initialized to avalue of 1. Then, from step (4222), or otherwise from step (4220), theprocess of steps (4208) through (4212) is repeated until, in step(4214), the iteration count is greater than or equal to the threshold,in which case, in step (4224), the charges are transferred from thebuffer row 366 to the serial register 344 and then output so as togenerate the image 356. Then, in step (4226), the second row counterKRow is incremented and the first row counter IRow is decremented. If,in step (4228), the value of the second row counter KRow is less thanthe number of rows NRow, then the process repeats with step (4210) untilthe entire image 356 has been transferred from the array 348 ofphotosites 346; otherwise, the process of recording and outputting animage 356 repeats with step (4202). Accordingly, the second row counterKRow provides for determining whether each row of the array 348 ofphotosites 346 has been recorded, the iteration count provides forrepetitively recording the entire array 348 of photosites 346 so as toaccumulate additional charge within each of the photosites 346, therebyimproving the associate ratio of charge (signal) to read noise, and thefirst row counter IRow provides for efficiently reading the array 348 ofphotosites 346.

Referring to FIGS. 43 a-e, a second embodiment of a CCD detector 164.1′comprises an imaging region 368 and a masked, frame-transfer region 370,wherein the frame-transfer region 370 provides for buffering the image356 so as to facilitate transfer thereof from the CCD detector 164.1′via a relatively slow serial register 344. Both the imaging region 368and the frame-transfer region 370 contain similar photosites 346 thatare adapted to store photo-generated charges, the difference being thatthe frame-transfer region 370 is masked from light, and thereby unableto generated photo-generated charges. Although the second embodiment ofthe CCD detector 164.1′ is suitable for use in any of theabove-described embodiments of the optical air data system 10, 10′, itwill now be described with particularity in cooperation with the opticalair data system 10′ illustrated in FIGS. 35-42, for example, incooperation with a second imaging process 4400 illustrated in FIG. 44.

Referring to FIGS. 43 a and 44, in step (4402), the photosites 364 inboth the imaging region 368 and the frame-transfer region 370 of the CCDdetector 164.1′ are initialized, for example, to a condition ofsubstantially zero charge, for example, as may result from an associatedread process of the CCD detector 164.1′. Then, in step (4404), insynchronism with the second laser beams 18 from the laser 12, for apulsed laser 12, an iteration count is initialized, e.g. to a value ofzero, wherein the iteration count is used to record the number of timesthe imaging region 368 has been recorded in subsequent steps. Then, instep (4406), the charges in the array 348 of photosites 346 are shifteddownwards, row by row, from the imaging region 368 into theframe-transfer region 370, through the recording zone 364 therebetween,wherein the photosites 346 in the recording zone 364 are exposed to thefirst 332.1, second 332.2, third 332.3 and fourth 332.4 linear fringepatterns, the light of which causes charges to be generated within theassociated photosites 346, which charges are then subsequently shifteddownwards. For example, FIG. 43 b illustrates a beginning stage of animage recording cycle, at which time the lowest row of photosites 346 ofthe imaging region 368 are recorded; FIG. 43 c illustrates anintermediate stage of the image recording cycle at which time a portionof the photosites 346 of the imaging region 368 have been recorded andthe charges therefrom have been shifted into the frame-transfer region370, and FIG. 43 d illustrates a final stage of the image recordingcycle at which time all of the photosites 346 of the imaging region 368have been recorded and the charges therefrom have been shifted into theframe-transfer region 370. Then, in step (4408), if the iteration countis less than a threshold, then, in step (4410), the iteration count isincremented, and, in step (4412), the charges are transferred from theframe-transfer region 370 back to the imaging region 368 of the CCDdetector 164.1′, after which the process repeats with step (4406) until,in step (4408), the iteration count is greater than or equal to thethreshold, after which, in step (4414), the charges are transferred fromthe frame-transfer region 370 to a frame buffer 372 via a serialregister 344 operatively associated with the frame-transfer region 370of the CCD detector 164.1′, as illustrated in FIG. 43 e, and then theprocess repeats with step (4402). Accordingly, the iteration countprovides for repetitively recording the imaging region 368 so as toaccumulate additional charge within each of the photosites 346 thereof,thereby improving the associate ratio of charge (signal) to read noise.The cumulative recording process is illustrated by the portions of theof the range-resolved fringe patterns 362.1, 362.2, 362.3 and 362.4 inFIGS. 43 b and 43 c with dashed outlines.

The range-resolved fringe patterns 362.1, 362.2, 362.3 and 362.4 in theimages 356 illustrated in FIGS. 41 and 43 e are simulations ofmeasurements from a high-altitude or space-based optical air data system10′ looking down on the atmosphere 24, wherein each range-resolvedfringe patterns 362.1, 362.2, 362.3 and 362.4 comprises a single fringe310. For the range-resolved fringe patterns 362.2, 362.3 and 362.4associated with the signal channels 122.1, 122.2 and 122.3, the widthand amplitude of the range-resolved fringe patterns 362.1, 362.2, 362.3and 362.4, i.e. the molecular signal component 310.2 thereof, increaseswith increasing range 46 corresponding to an increase in density andtemperature with decreasing altitude in the atmosphere 24, whereas therange-resolved fringe patterns 362.1 associated with the referencechannel 120 exhibits a substantially constant width.

Referring to FIG. 45, in accordance with an alternative embodiment of anoptical air data system 10″, the reference channel 120 can bemultiplexed with one or more signal channels 122.1, 122.2 and 122.3 soas to provide for eliminating the separate and distinct processing ofthe reference channel 120 by the optical air data system 10″. Forexample, in accordance with a first embodiment of an optical multiplexer374.1, the fiber optic 76.1 of the reference channel 120 is bunchedtogether with the fiber optic 76.2, 76.3, 76.4 of one of the signalchannels 122.1, 122.2 or 122.3 so that the light 376.1, 376.2 from thereference 120 and signal 122.1, 122.2, 122.3 channels illuminates acommon region of the Fabry-Pérot interferometer 78 as a multiplexed beamof light 376. As another example, in accordance with a second embodimentof an optical multiplexer 374.2, light 376.1 from the fiber optic 76.1of the reference channel 120 is combined with light 376.2 from a fiberoptic 76.2, 76.3, 76.4 of one of the signal channels 122.1, 122.2 or122.3 using a beam splitter 378 so as to form a multiplexed beam oflight 376, which is then collected into a fiber optic 380 by alight-collecting element 382, for example, a GRIN lens or an asphericlens, and directed therethrough to the Fabry-Pérot interferometer 78. Asyet another example, in accordance with a third embodiment of an opticalmultiplexer 374.3, light 376.1 from the fiber optic 76.1 of thereference channel 120 is combined with light 376.2 from a fiber optic76.2, 76.3, 76.4 of one of the signal channels 122.1, 122.2 or 122.3using a beam splitter 378 so as to form a multiplexed beam of light 376,which is directed via an associated optical path to the Fabry-Pérotinterferometer 78, either directly, or indirectly using one or moreassociated mirrors.

The multiplexed beam of light 376 is processed by the Fabry-Pérotinterferometer 78, transformed into an associated linear fringe pattern332.2, 332.3 or 332.4 by the associated bi-CLIO 312, and imaged onto anassociated CCD detector 164.1, 164.1′ which provides for generating anassociated range-resolved fringe pattern 362.2, 362.3 or 362.4, whereinthe information associated with the zero or near-zero range portionthereof corresponds to the reference channel 120, and the remaininginformation corresponds to the associated signal channel 122.1, 122.2 or122.3. Although FIG. 45 illustrates three multiplexed channels, so as toillustrate the three different associated optical multiplexers 374.1,374.2 and 374.3, it should be understood that the optical air datasystem 10″ can function using only one optical multiplexer 374.1, 374.2or 374.3 to provide the information from the reference channel 120.

Referring to FIGS. 3 and 4, the optical air data systems 10′, 10″ thatprovide for range-resolved imaging and associated range-resolved airdata products can be adapted to incorporate or cooperate with either abiaxial system 50, e.g. as illustrated in FIG. 3, or a coaxial system66, e.g. as illustrated in FIG. 4, wherein different rows in the image356 of the range-resolved fringe patterns 362.2, 362.3 and 362.4 areassociated with different range-separated measurement volumes 311 withinthe associated interaction regions 30.

Referring to FIG. 46, in accordance with alternative embodiments, anoptical air data system 10′″ in a biaxial system 50 configuration may beadapted with a plurality of different fields of view 32, each of whichcooperates with a common line of sight 40 of an associated second laserbeam 18. A telescope 26 and an associated final light-collecting element72 is adapted for each associated field of view 32 to collect associatedlight signals 44 backscattered from associated interaction regions 30defined by the intersection of the associated field of view 32 with thesecond laser beam 18 along the line of sight 40. Each of the lightsignals 44 associated with the different fields of view 32 are thenprocessed by an associated Fabry-Pérot interferometer 78, detectionsystem 80, and data processor 198 as separate signal channels 122,together with an associated reference channel 120 of an associatedreference beam 16, as described hereinabove for the previously describedembodiments.

In accordance with one aspect, the different fields of view 32 may beassociated with corresponding different ranges along the line of sight40. For example, for a line of sight 40 spanning a range of altitudes,each different field of view 32 provides for measuring an associated setof air data products at a corresponding different altitude. In oneembodiment, for example, a first final light-collecting element 72.1 incooperation with a first telescope 26.1 aligned with a first axis 32.1′associated with a first field of view 32.1 provides for collectingbackscattered light signals 44 from a first interaction region 30.1located at a first range from the beam splitter optic 20 from which thesecond laser beam 18 originates. A second final light-collecting element72.2 at a first light-collecting location in cooperation with a secondtelescope 26.2 aligned with a second axis 32.2′ associated with a secondfield of view 32.2 provides for collecting backscattered light signals44 from a second interaction region 30.2 located at a second range fromthe beam splitter optic 20. A third final light-collecting element 72.3at a second light-collecting location in cooperation with the secondtelescope 26.2 aligned with a third axis 32.3′ associated with a thirdfield of view 32.3 provides for collecting backscattered light signals44 from a third interaction region 30.3 located at a third range fromthe beam splitter optic 20. For example, in one embodiment, the firstand second light-collecting locations associated with the secondtelescope 26.2 are transversely offset from one another in the focalplane 386 of the associated lens system 74 of the second telescope 26.2,the first and second light-collecting locations thereby defining thecorresponding associated second 32.2 and third 32.3 fields of view. Itshould be understood that the particular plurality of finallight-collecting element 72 associated with a particular telescope 26 isnot limiting, i.e. the actual number being limited by the physical sizeof the final light-collecting elements 72 and the size of the associatedlens system 74.

In accordance with another aspect, the different fields of view 32 maybe associated with a common interaction region 30 along the line ofsight 40, for example, so as to provide for measuring differentline-of-sight relative wind velocities U in different directionsrelative to a common region of the atmosphere 24, so that relative to aninertial frame of reference, each measurement is affected bysubstantially the same wind velocity of the atmosphere relative to theinertial frame of reference, so as to improve the accuracy of anassociated relative wind vector calculated from the associated line-ofsight-relative wind velocities U. In one embodiment, for example, afirst final light-collecting element 72.1 in cooperation with a firsttelescope 26.1 aligned with a first axis 32.1′ associated with a firstfield of view 32.1 provides for collecting backscattered light signals44 from a first interaction region 30.1, and a fourth finallight-collecting element 72.4 in cooperation with a third telescope 26.3aligned with a fourth axis 32.4′ associated with a fourth field of view32.4 also provides for collecting backscattered light signals 44 fromthe first interaction region 30.1, but from a different direction, sothat the light signals 44 from the first 72.1 and fourth 72.4 finallight-collecting elements provide for measuring line-of-sight relativewind velocities U in different directions so as to provide for measuringan associated relative wind vector. The first 72.1 and fourth 72.4 finallight-collecting elements in the embodiment illustrated in FIG. 46provide for determining an associated 2-D relative wind vector in theplane defined by the first 32.1′ and fourth 32.4′ axes. An additionalout-of-plane final light-collecting element 72 in cooperation with anassociated telescope 26 having an associated field of view 32 alsoaligned with the first interaction region 30.1 may be used to providefor determining an associated 3-D relative wind vector.

Referring to FIG. 47, an optical air data system 10″″ may be adapted tomeasure the overall intensity of the reference beam 16 with a detector388, rather than processing the reference beam through the Fabry-Pérotinterferometer 78, so as to provide for either reducing the total numberof channels processed with the Fabry-Pérot interferometer 78, or so asto provide for processing an addition signal channel 122 therewith. Suchan arrangement would be suitable when the associated air data productsbeing measured therewith are not dependent upon relative wind velocity,the latter of which measure is calibrated responsive to a measure offrequency shift of the reference channel 120 using the Fabry-Pérotinterferometer 78. For example, the optical air data system 10″″illustrated in FIG. 47 would be suitable for measuring either or both ofstatic density ρ and static temperature T_(S), or to provide forderiving therefrom one or more of static air pressure, total airtemperature, speed of sound, air density ratio or pressure altitude.

Heretofore the laser 12 has been assumed to be a generic device capableof providing sufficiently narrow-band photonic radiation at an operativefrequency so as to provide for an operative optical air data system 10,10′, 10″, 10′″, 10″″. For example, a Nd:YAG laser 12.1 can operate atrelatively high power levels so as to provide sufficiently intenseillumination so as to provide for relatively long range atmosphericsensing applications. An Nd:YAG laser 12.1 has a fundamental wavelengthof 1064 nanometers (nm), from which shorter wavelengths/higherfrequencies may be generated using one or more harmonic generatorsoperatively associated with or a part of the Nd:YAG laser 12.1. Forexample, a second-harmonic generator could be used to convert thefundamental 1064 nm light to second-harmonic 532 nm light which couldthen be transformed with either a third- or fourth-harmonic generator togenerate associated 355 nm or 266 nm light respectively. Heretoforethese second-, third- and/or fourth-harmonic generators would be eitherincorporated in, or free-space coupled to, the laser 12 generally or,more particularly, the Nd:YAG laser 12.1.

As noted hereinabove, ultraviolet light—e.g. 266 nm or 355 nm light thatcan be generated as described hereinabove—can be suitable foratmospheric sensing applications. One problem associated withultraviolet light when transmitted or distributed through associatedfiber optics 76 of the optical air data system 10, 10′, 10″, 10′″, 10″″is the resulting degradation of the associated fiber optics 76, forexample, that can occur as a result of a power per unit area thereinexceeding a damage threshold, e.g. at a focal point within the fiberoptics 76, or a solarization of the fiber optics 76. However, the fiberoptics 76 provide for locating relatively sensitive portions of theoptical air data system 10, 10′, 10″, 10′″, 10″″, e.g. the laser 12,Fabry-Pérot interferometer 78, and detection system 80, at a relativelysecure location that may be relatively remote from the associatedoptical head 22 containing the associated beam splitter optics 20, beamsteering optics 210, and telescope(s) 26, by providing for efficientlytransmitting the associated first 14 and/or second 18 laser beams,and/or the reference beam 16 to the optical head 22, and fortransferring the received light signals 44 from the optical head 22 tothe Fabry-Pérot interferometer 78.

Referring to FIG. 48, an optical air data system 10, 10′, 10″, 10′″,10″″ may be adapted to operate at ultraviolet frequencies without theill affects of associated solarization or power-induced damage of anassociated fiber optic 304 coupling the relatively high-power firstlaser beam 14 operating at a fundamental harmonic to the associatedoptical head 22 by transmitting relatively long-wavelength laser lightfrom the laser 12 through a fiber optic 304 to an associated harmonicgenerator 390, generating relatively shorter-wavelength light with theharmonic generator 390, and then transmitting through free space therelatively shorter-wavelength light from the harmonic generator 390 tothe beam splitter optic 20 of the optical head 22. The harmonicgenerator 390 could be incorporated in the optical head 22 so as toprovide for optical alignment therewith and ruggedization of theassociated harmonic generator 390. Accordingly, this arrangementprovides for operation at ultraviolet frequencies and the use of fiberoptics 304, 76 to mechanically isolate of the laser 12, Fabry-Pérotinterferometer 78, and detection system 80 from the optical head 22,without a substantial prospect of solarization-induced degradation ofthe fiber optic 304 carrying the relatively high-power laser light fromthe laser 12 to the optical head 22.

For example, referring to FIG. 49 a, in accordance with a firstembodiment, a Nd:YAG laser 12.1 is operatively coupled to a Type 1second-harmonic generator 390.1 with a fiber optic 304, wherein the Type1 second-harmonic generator 390.1 provides for converting the 1064 nmlaser light from the Nd:YAG laser 12.1 to 532 nm light, which is thenoperatively coupled over free space to a fourth-harmonic generator 390.2that provides for converting the 532 nm light from the Type 1second-harmonic generator 390.1 to 266 nm light of the first laser beam14. The Type 1 second-harmonic generator 390.1 and the fourth-harmonicgenerator 390.2 comprise crystals, for example, BBO, KDP and LBO, theselection of which depends upon the manufacturer and various factors,e.g. pulse energy. The crystal used in the Type 1 second-harmonicgenerator 390.1 is cut in accordance with what is known as a Type 1 cutso as to provide for two photons of 532 nm light to be doubled to 266 nmlight by the fourth-harmonic generator 390.2. For example, in oneembodiment, the Nd:YAG laser 12.1 can be a model 8030 manufactured byContinuum, which operates in cooperation with a Continuum Part No.617-8000 Type 1 second-harmonic generator 390.1 and a Continuum Part No.617-8140 fourth-harmonic generator 390.2. The Nd:YAG laser 12.1 can beeither flash-lamp pumped or diode-pumped.

As another example, referring to FIG. 49 b, in accordance with a secondembodiment, a Nd:YAG laser 12.1 is operatively coupled to a Type 2second-harmonic generator 390.1′ with a fiber optic 304, wherein theType 2 second-harmonic generator 390.1′ provides for converting the 1064nm laser light from the Nd:YAG laser 12.1 to 532 nm light, which is thenoperatively coupled over free space to a third-harmonic generator 390.2′that provides for converting the 532 nm light from the Type 2second-harmonic generator 390.1′ to 355 nm light of the first laser beam14. The Type 2 second-harmonic generator 390.1′ and the third-harmonicgenerator 390.2′ comprise crystals, for example, BBO, KDP and LBO, theselection of which depends upon the manufacturer and various factors,e.g. pulse energy. The crystal used in the Type 2 second-harmonicgenerator 390.1′ is cut in accordance with what is known as a Type 2 cutso as to provide for one photon of 532 nm light to be mixed with onephoton of 1064 nm light by the third-harmonic generator 390.2′ so as togenerate a corresponding photon of 355 nm light. For example, in oneembodiment, the Nd:YAG laser 12.1 can be a model 8030 manufactured byContinuum, which operates in cooperation with a Continuum Part No.617-9100 Type 2 second-harmonic generator 390.1′ and a Continuum PartNo. 617-8020 third-harmonic generator 390.2′. The Nd:YAG laser 12.1 canbe either flash-lamp pumped or diode-pumped.

Accordingly, in the first and second embodiments illustrated in FIGS. 49a and 49 b respectively, the fundamental 1064 nm laser light from theNd:YAG laser 12.1 is transmitted via a fiber optic 304 to harmonicgenerators 390.1, 390.2 or 390.1′, 390.2′ that can be located remotelyrelative to the Nd:YAG laser 12.1, for example, in the optical head 22,and ultraviolet light generated by the harmonic generators 390.2 or390.2′ is thereafter transmitted through free space. The 1064 nm laserlight transmitted through the fiber optic 304 does not result in anysubstantial degradation thereof.

As yet another example, referring to FIG. 49 c, in accordance with athird embodiment—a modification of either the first or secondembodiments,—the Nd:YAG laser 12.1 is operatively coupled to theassociated Type 1 390.1 or Type 2 390.1′ second-harmonic generator witha first fiber optic 304.1, and the Type 1 390.1 or Type 2 390.1′second-harmonic generator is operatively coupled to the associatedfourth-390.2 or third-390.2′ harmonic generator, respectively, with asecond fiber optic 304.2, so that the first fiber optic 304.1 transmitsfundamental 1064 nm laser light, and the second fiber optic 304.2transmits 532 nm laser light, neither of which results in anysubstantial degradation of the associated first 304.1 or second 304.1fiber optics.

As yet another example, referring to FIG. 49 d, in accordance with afourth embodiment—a modification of either the first or secondembodiments,—the Nd:YAG laser 12.1 is operatively coupled to theassociated Type 1 390.1 or Type 2 390.1′ second-harmonic generator viafree space, and the Type 1 390.1 or Type 2 390.1′ second-harmonicgenerator is operatively coupled to the associated fourth-390.2 orthird-390.2′ harmonic generator, respectively, with a fiber optic 304,so that the fiber optic 304 transmits 532 nm laser light which does notresult in any substantial degradation thereof. For example, the Type 1390.1 or Type 2 390.1′ second-harmonic generator could be eitherattached to, located within, or otherwise a part of the Nd:YAG laser12.1.

The fiber optics 304, 304.1, 304.2 used in the first through fourthembodiments of FIGS. 49 a-d may comprise either single optical fibers orbundles of optical fibers. An optics assembly 392 operatively associatedat each end of the associated fiber optics, i.e. at each of the entranceand exit ends, provides for focusing and/or collimating and/or otherwiseshaping the associated beam of laser light into or out of the associatedfiber optics 304, 304.1, 304.2 so as to provide for efficientlytransferring light from the laser 12, 12.1 to the associated first laserbeam 14. The optics assembly 392 may or may not be integrated with theassociated fiber optics 304, 304.1, 304.2, and may or may not behermetically sealed at the associated fiber interface.

Referring to FIG. 50, various optical air data systems 10, 10′, 10″,10′″, 10″″ can be used in a variety of applications, including flightcontrol or flight data monitoring, for example, for an aircraft 38 orUAV 394; or monitoring atmospheric or weather conditions from anaircraft 38.1, 38.2, UAV 394, balloon 396, satellite 398, orground-based LIDAR system 400,

For example, the aircraft 38, 38.1 and UAV 394 illustrated in FIG. 50each incorporate a first optical air data system 10.1 that incorporatesthree lines of sight 40 so as to provide for measuring an associatedrelative wind vector in addition to other air data products. Generallythe optical air data system 10 can be adapted for airframe applicationswhich, for example, might otherwise incorporate a pitot-static tube formeasuring air speed. In addition to air speed, the optical air datasystem 10 provides for optically measuring, or calculating from opticalmeasurements, a substantial quantity of air data products, and can beadapted to detect wind shear, wake vortices, clear air turbulence, andengine stall (unstart) conditions. Common air data products include, butare not limited to, Mach number, true airspeed, calibrated airspeed,vertical speed, static density, static air temperature, sideslip, angleof attack, pressure altitude, and dynamic pressure. The air dataproducts can be used directly by an aircraft flight computer for flightcontrol purposes. The optical air data system 10 provides for anairframe-independent design that can be flush-mounted to the skin of theairframe, e.g. without protrusions that otherwise might increase theairframe's radar cross section and drag, so as to provide for relativelylow observability and drag. The optical air data system 10 can operateat substantial angles of attack. For example, a properly-configuredoptical air data system 10 can operate at a 90 degree angle of attack.The optical air data system 10 can be adapted to a variety of airframes,for example, including highly maneuverable aircraft and hoverableaircraft. The optical air data system 10 provides for anairframe-independent design that can be relatively inexpensive tocalibrate, recalibrate or service.

As another example, the aircraft 38, 38.1, 38.2, UAV 394, and balloon396 illustrated in FIG. 50 each incorporate a second optical air datasystem 10.2 adapted with a plurality of lines of sight 40, so as toprovide for substantially simultaneously measuring air data productsfrom one or more interaction regions 30 along each of the associatedlines of sight 40. For example, the first aircraft 38.1 incorporates twolines of sight 40 distributed transversely with respect to theassociated direction of travel thereof, and the second aircraft 38.2incorporates five lines of sight 40 distributed transversely withrespect to the associated direction of travel thereof, so as to providefor automatically acquiring a substantial amount of atmospheric data(e.g. density, temperature and wind velocity) that can be used foreither monitoring or predicting weather, or for monitoring particularemissions into the atmosphere. In accordance with another embodiment,the UAV 394 is illustrated with lines of sight 40 substantially alongthe direction of travel thereof, which can provide for automaticallyacquiring a substantial amount of atmospheric data (e.g. density,temperature and wind velocity) that, for example, can be used for eithermonitoring or predicting weather dynamics, or for monitoring thedynamics of particulate emissions into the atmosphere. Generally, theorientation of the plurality of lines of sight 40 relative to theassociated vehicle or the associated direction of travel thereof is notlimiting, i.e. either other orientations or a combination oforientations may be used.

As yet another example, the satellite 398 and the ground-based LIDARsystem 400 illustrated in FIG. 50 each incorporate a third optical airdata system 10.3 adapted with a line of sight 40 that is directedrespectively downwards or upwards into the atmosphere so as to providefor measuring air data products from one or more interaction regions 30along each of the associated one or more lines of sight 40, for example,so as to provide for automatically acquiring a substantial amount ofatmospheric data (e.g. density, temperature and wind velocity) that canbe used for either monitoring or predicting weather, or for monitoringparticular emissions into the atmosphere.

Referring to FIG. 51, and as illustrated in FIG. 50 for the satellite398 and the ground-based LIDAR system 400, the third optical air datasystem 10.3 may be operatively associated with a gimbal mechanism 402comprising an azimuthally-rotatable platform 404 which is adapted topivotally support an optical head 22 so as to provide for an elevationalrotation thereof relative a base 406 to which the azimuthally-rotatableplatform 404 is operatively associated. Accordingly, theazimuthally-rotatable platform 404 is adapted to rotate relative to thebase 406, for example, responsive to an associated motor drive system,so as to define an associated azimuth angle 408 of the optical head 22,and the optical head 22 is adapted to rotate relative to theazimuthally-rotatable platform 404, for example, responsive to anassociated motor drive system, so as to define an associated elevationangle 410 of the optical head 22. Accordingly, coordinated rotations ofthe optical head 22 in both azimuth 408 and elevation 410 angle providefor acquiring associated optical air data from associated interactionregions 30 of an associated spherical shell of the atmosphere 24. Theoptical air data system 10.3 may provide for a plurality or range ofinteraction regions 30 associated with the associated second laser beam18 so as to provide for sampling optical air data from a correspondingplurality of spherical shells. Referring to FIG. 50, in one embodimentillustrated in cooperation with the ground-based LIDAR system 400, thelaser 12, interferometer 78 and detector system 80 of the optical airdata system 10.3 may be mounted on the associated azimuthally-rotatableplatform 404 so as to rotate therewith, wherein the laser 12 andinterferometer 78 are operatively coupled to the associated optical head22 with an associated fiber-optic bundle 76′. The base 406 of the gimbalmechanism 402 of the ground-based LIDAR system 400 is adapted to providefor mobile operation thereof. The base 406 of the gimbal mechanism 402of the satellite 398 is operatively coupled to the satellite 398 so asto provide for scanning the optical head 22, for example, as thesatellite 398 travels in its orbit.

It should be understood that any of the optical air data systems 10.2,10.3 illustrated in FIG. 50 can be operatively associated with any ofthe associated platforms (i.e. aircraft 38.1, 38.2, UAV 394, balloon396, satellite 398, or ground-based LIDAR system 400) or otherplatforms. For example, the satellite 398 could incorporate an opticalair data system 10.2 comprising a plurality of lines of sight 40arranged transverse to the direction of travel. For example, in oneembodiment, eight lines of sight 40 are contemplated. As anotherexample, the balloon 396 could incorporate an optical air data system10.2 with a single line of sight 40, possibly operatively associatedwith a gimbal system 402. As another example, an optical head 22operatively associated with a gimbal system 402 could incorporate aplurality of lines of sight 40 and could provide for eitherrange-resolved imaging or a plurality of interaction regions 30 and aplurality of associated light signals 44 associated with a given line ofsight 40.

Accordingly, the optical air data system 10, 10′, 10″, 10′″, 10″″ can beadapted to measure air data products on a variety of platforms, forexample, including, but not limited to, satellites 398, aircraft 38,UAVs 394, glide weapon systems, ground-based platforms (stationary ormobile), and watercraft. The optical air data system 10, 10′, 10″, 10′″,10″″ can be adapted to measure air data products of a variety ofatmospheres 24, for example, that of the Earth or other planetary orcelestial bodies, or can be adapted to measure or map air data productsof fields within a wind tunnel or surrounding an aerodynamic body duringthe operation thereof. Furthermore, although one embodiment usesultraviolet (UV) laser light, the optical air data system 10 can operateover a large range of wavelengths spanning from the visible down to theultraviolet. The ultraviolet light provides additional stealthcharacteristics for the system because the light is quickly absorbed bythe atmosphere 24, and is not otherwise easily detected from relativelylong-range distances. However, the optical air data system 10 can alsooperate in other wavelength regions, such as longer ultravioletwavelengths or even visible wavelengths. For example, a variety oflasers 12 can be used, including, but not limited to: Ruby (694 nm);Neodymium-based lasers: Nd:YAG, Nd:Glass (1.062 microns, 1.054 microns),Nd:Cr:GSGG, Nd:YLF (1.047 and 1.053 microns), Nd:YVO (orthovanadate,1.064 microns); Erbium-based lasers: Er:YAG and Er:Glass;Ytterbium-based lasers: Yb:YAG (1.03 microns); Holmium-based lasers:Ho:YAG (2.1 microns); Thulium-based lasers: Tm:YAG (2.0 microns); andtunable lasers: Alexandrite (700-820 nm), Ti:Sapphire (650-1100 nm), andCr:LiSAF. The associated laser 12 can be either pulsed—at any PulseRepetition Frequency (PRF)—or continuous wave (CW).

While specific embodiments have been described in detail in theforegoing detailed description and illustrated in the accompanyingdrawings, those with ordinary skill in the art will appreciate thatvarious modifications and alternatives to those details could bedeveloped in light of the overall teachings of the disclosure.Accordingly, the particular arrangements disclosed are meant to beillustrative only and not limiting as to the scope of the invention,which is to be given the full breadth of the appended claims and any andall equivalents thereof.

1. An optical air data system, comprising: a. a reference beam from afirst beam of light generated by a laser; b. at least one second beam oflight from said first beam of light, wherein said at least one secondbeam of light is directed into an atmosphere along an associated axis;c. at least one telescope adapted to receive light backscattered bymolecules or aerosols of said atmosphere responsive to a correspondingat least one said second beam of light, wherein at least one saidtelescope comprises a plurality of light collectors, each of saidplurality of light collectors is located at a different transverselocation relative to an optic axis of said at least one said telescope,and each of said plurality of light collectors provides for collectinglight backscattered from a different region along one said second beamof light associated with said at least one said telescope; d. aninterferometer, wherein a first portion of said interferometer isadapted to receive a light signal from said light backscattered by saidmolecules or aerosols of said atmosphere, at least one second portion ofsaid interferometer is adapted to receive at least one of said referencebeam and at least one other light signal from said light backscatteredby said molecules or aerosols of said atmosphere, said interferometer isoperative to generate a first fringe pattern associated with said lightsignal from said light backscattered by said molecules or aerosols ofsaid atmosphere, and said interferometer is operative to generate atleast one second fringe pattern associated with said at least one ofsaid reference beam and at least one other light signal from said lightbackscattered by said molecules or aerosols of said atmosphere; and e.at least one detector, wherein said at least one detector is adapted todetect said first fringe pattern and said at least one second fringepattern, and said at least one detector is adapted to output acorresponding resulting at least one signal.
 2. An optical air datasystem as recited in claim 1, wherein said plurality of light collectorsare located proximate to a focal plane of said at least one saidtelescope.
 3. An optical air data system as recited in claim 1, whereinsaid light received by said at least one telescope is backscatteredeither by said molecules of said atmosphere or by said aerosols of saidatmosphere, or said light received by said at least one telescope isbackscattered by both said molecules and said aerosols of saidatmosphere.
 4. An optical air data system, comprising: a. a referencebeam from a first beam of light generated by a laser; b. at least onesecond beam of light from said first beam of light, wherein said atleast one second beam of light is directed into an atmosphere along anassociated axis; c. a plurality of telescopes adapted to receive lightbackscattered by molecules or aerosols of said atmosphere responsive toa corresponding at least one said second beam of light, wherein at leasttwo of said plurality of telescopes are each associated with a commonsaid at least one second beam of light; d. an interferometer, wherein afirst portion of said interferometer is adapted to receive a lightsignal from said light backscattered by said molecules or aerosols ofsaid atmosphere, at least one second portion of said interferometer isadapted to receive at least one of said reference beam and at least oneother light signal from said light backscattered by said molecules oraerosols of said atmosphere, said interferometer is operative togenerate a first fringe pattern associated with said light signal fromsaid light backscattered by said molecules or aerosols of saidatmosphere, and said interferometer is operative to generate at leastone second fringe pattern associated with said at least one of saidreference beam and at least one other light signal from said lightbackscattered by said molecules or aerosols of said atmosphere; and e.at least one detector, wherein said at least one detector is adapted todetect said first fringe pattern and said at least one second fringepattern, and said at least one detector is adapted to output acorresponding resulting at least one signal.
 5. An optical air datasystem as recited in claim 4, wherein said light received by said atleast one telescope is backscattered either by said molecules of saidatmosphere or by said aerosols of said atmosphere, or said lightreceived by said at least one telescope is backscattered by both saidmolecules and said aerosols of said atmosphere.
 6. An optical air datasystem as recited in claim 4, wherein associated fields of view of atleast two of said plurality of telescopes overlap with one said secondbeam of light at a corresponding plurality of regions of overlap, atleast a portion of said light backscattered by said molecules oraerosols of said atmosphere is generated within each of said pluralityof regions of overlap, and each of said at least two of said pluralityof telescopes receives at least a portion of said light backscattered bysaid molecules or aerosols of said atmosphere within a correspondingregion of overlap of said plurality of regions of overlap.
 7. An opticalair data system as recited in claim 6, wherein said light received bysaid at least one telescope is backscattered either by said molecules ofsaid atmosphere or by said aerosols of said atmosphere, or said lightreceived by said at least one telescope is backscattered by both saidmolecules and said aerosols of said atmosphere.
 8. An optical air datasystem as recited in claim 4, wherein associated fields of view of atleast two of said plurality of telescopes overlap with one said secondbeam of light at a substantially common region of overlap, at least aportion of said light backscattered by said molecules or aerosols ofsaid atmosphere is generated within said substantially common region ofoverlap, and each of said at least two of said plurality of telescopesreceives at least a portion of said light backscattered by saidmolecules or aerosols of said atmosphere within said substantiallycommon region of overlap.
 9. An optical air data system as recited inclaim 8, wherein said light received by said at least one telescope isbackscattered either by said molecules of said atmosphere or by saidaerosols of said atmosphere, or said light received by said at least onetelescope is backscattered by both said molecules and said aerosols ofsaid atmosphere.
 10. An optical air data system, comprising: a. areference beam from a first beam of light generated by a laser; b. atleast one second beam of light from said first beam of light, whereinsaid at least one second beam of light is directed into an atmospherealong an associated axis; c. at least one telescope adapted to receivelight backscattered by molecules or aerosols of said atmosphereresponsive to a corresponding at least one said second beam of light; d.a gimble mount, wherein said gimble mount provides for operativelycoupling said at least one telescope and at least one beam steeringelement to a base, wherein said at least one beam steering elementprovides for steering said at least one second beam of light, and saidgimble mount provides for positioning at least one region of overlap ofsaid at least one second beam of light with at least one field of viewof said at least one telescope; e. an interferometer, wherein a firstportion of said interferometer is adapted to receive a light signal fromsaid light backscattered by said molecules or aerosols of saidatmosphere, at least one second portion of said interferometer isadapted to receive at least one of said reference beam and at least oneother light signal from said light backscattered by said molecules oraerosols of said atmosphere, said interferometer is operative togenerate a first fringe pattern associated with said light signal fromsaid light backscattered by said molecules or aerosols of saidatmosphere, and said interferometer is operative to generate at leastone second fringe pattern associated with said at least one of saidreference beam and at least one other light signal from said lightbackscattered by said molecules or aerosols of said atmosphere; and f.at least one detector, wherein said at least one detector is adapted todetect said first fringe pattern and said at least one second fringepattern, and said at least one detector is adapted to output acorresponding resulting at least one signal.
 11. An optical air datasystem as recited in claim 10, wherein said light received by said atleast one telescope is backscattered either by said molecules of saidatmosphere or by said aerosols of said atmosphere, or said lightreceived by said at least one telescope is backscattered by both saidmolecules and said aerosols of said atmosphere.
 12. An optical air datasystem as recited in claim 10, wherein said gimble mount provides forazimuthally scanning said at least one region of overlap.
 13. An opticalair data system as recited in claim 10, wherein said base is operativelycoupled to a land, air, space or water vehicle.
 14. An optical air datasystem as recited in claim 10, wherein said gimble mount provides forelevationally scanning said at least one region of overlap.
 15. Anoptical air data system as recited in claim 10, wherein said laser, saidinterferometer and said at least one detector are operatively coupled toan azimuthally-rotatable platform of said gimble mount.